Archive for the ‘botany’ Category

The Ghost Boundary of the Last Glacial Maximum Ice Margin

March 30, 2017

The southern margin of the Laurentide Ice Sheet is still evident today in the range maps of at least 19 species of eastern trees.  During the most recent Ice Age about 20,000 years ago glaciers advanced to their farthest extent, a time period known as the Last Glacial Maximum (LGM). This giant sheet of ice pushed boulders, obliterated forests, and even blocked and bent major rivers.  After the glacier began retreating many species of plants colonized the nearby deglaciated territory, but 19 species of trees never advanced and remain locked in the same ranges within which they probably occurred during the Ice Age.    Though the ice margin is long gone it still marks the northern limit of these trees, serving as a kind of ghost boundary.

A majority of paleoecologists long thought a boreal forest consisting of spruce and northern species of pine existed for hundreds of miles south of the ice sheet during the LGM. Studies of fossil pollen abundance deceptively support this belief.  Spruce pollen dating to the LGM predominates in sites as far south as north Georgia.  But spruce and pine trees produce more pollen than oak and other hardwood species. Moreover, spruce and pine pollen is more resistant to decay, so oak pollen is likely underrepresented in samples.  The range maps of the below listed 19 species suggests they occurred all the way up to the ice margin during the LGM.  The forest that existed immediately south of the ice sheet during the Ice Age was probably a strange mix of spruce and hardwood trees not found in any extant natural community.  Sweet gum, post oak, and river birch grew side by side with white spruce and fir.    Scientists refer to this unusual plant composition as “non analogue” communities.  Farther south, spruce pollen excavated from fossil sites likely originated from the extinct temperate species–Critchfield’s spruce.

Below is the list of 19 species whose northern range limit reaches the ghost boundary of the Laurentide Glacier.  This list is from the below referenced study.

shortleaf pine (Pinus echinata)

Virginia pine (P. virginiana)

pitch pine (P. rigida)

sourwood (Oxydendrum arboreum)

willow oak (Quercus phyllos)

southern red oak (Q. falcata)

swamp chestnut oak (Q. michauxii)

overcup oak (Q. lyrata)

post oak (Q. stellata)

yellow buckeye (Aescules flava)

river birch (Betula nigra)

persimmon (Diospyros virginiana)

pecan (Carya illinoinensis)

pumpkin ash (Fraxinus profunda)

sugarberry (Celtis laevigata)

winged elm (Ulmus alata)

sweetgum (Liquidamber styraciflua)

white basswood (Tilia heterophylla)

black locust (Robinia pseudoacacia)

Image result for Laurentide Glacier during LGM

Map of the Laurentide Ice Sheet.  The northern limits of at least 19 species of eastern trees coincides with the ice margin of this glacier where it advanced during the Last Glacial Maximum about 20,000 years ago.

Image result for shortleaf pine range map

Range map of shortleaf pine.   The northern limit of this species closely coincides with where the southern lobe of the Laurentide Glacier advanced.

Image result for sourwood range map

Sourwood range map.

Image result for willow oak range map

Willow oak range map.  Note how it grows to southern New Jersey, just short of where the ice sheet advanced.

Image result for yellow buckeye range map

Yellow buckeye range map.

Liquidambar styraciflua range map 4.png

Sweetgum range map.

When I was researching this blog article, I discovered a 20th species that might be added to this list.  Blackjack oak (Q. marilandica) is a small scrubby oak that grows on poor sandy soils.  The northern limit of this species range also is nearly identical with the ghost boundary of the Laurentide Glacier.  However, there are 2 small disjunct populations of this species in southern Michigan.  Unlike the other 19 species on this list blackjack oak must have temporarily colonized deglaciated territory, thriving on poor gravelly soils recently scoured by glaciers.  After soil improved other species outcompeted blackjack oak over most of the Midwest, but it remains in locally favorable habitat

Reference:

Loehle, C; and H. Iltis

“The Pleistocene Biogeography of Eastern North America: A Nonmigration Scenario for Deciduous Forest”

U.S. Department of Energy Technical Report 1998

https://www.osti.gov/scitech/biblio/564104

Pleistocene Pecans (Carya illinoinensis)

November 20, 2016

The pecan tree is 1 of 17 species of hickory trees.  Hickories are native to North America and Asia and formerly occurred in Europe, but Ice Ages, beginning about 2.5 million years ago, wiped them out there.  European mountains have an east to west orientation, while American mountains are oriented north to south.  Hickories prefer temperate climates, and the east-west mountains blocked their retreat in Europe during glacial expansions.  This explains why hickories and so many other tree species survived Ice Ages in North America but not in Europe.

Evidence of fossil pollen grains suggests hickory trees grew alongside dinosaurs during the late Cretaceous, though the oldest fossil hickory nut dates to about 34 million years ago.  Most early hickory species had thin shells, but they evolved thicker shells about 38 million years ago in response to the evolution of tree squirrels.  Squirrels love the nutrient rich nuts, so hickories evolved nuts with thicker shells, and the squirrels in turn evolved greater gnawing power.  Evolution is a constant struggle.  However, pecans retained the thinner shells of their early ancestors.  This puzzled me because it seems as if squirrels would have eliminated all hickory species with thinner shells because they were easier to exploit.  I wondered if pecans were a recent species, cultivated and spread by Native Americans.  I’ve concluded however, based on certain lines of evidence, that pecans are an ancient species of hickory, not a recently evolved species manipulated by man.

Wild Pecan Tree

Wild pecan tree.

{The native range of Carya illinoensis}

Native range of wild pecan trees.  Man has greatly expanded this range by planting pecan orchards.  Georgia is now the leading producer of pecans, though they are not native to this state.  Pecans need longer growing seasons than other species of hickory because their nuts mature later.

Genetic studies determined pecans have a large genetic diversity within populations.  If pecans descended from human cultivation, they would have low genetic diversity because they would descend from a small population initially cultivated by man.  I was also mistaken in considering squirrels the only major predator of hickory nuts.  The pecan weevil ( Curculio caryae ) infests all species of hickories, and pecan trees growing in mixed stands with other hickory species have an advantage over their cousins.  Pecans mature later in the season than other species of hickory.  The pecan weevil hatches and emerges in August and will infest whichever hickories have developed kernels.  Because thick shelled hickories mature before thin-shelled pecans, the pecan weevil will infest them first and go through their life cycle without ever infesting the thin-shelled pecan.  Weevils will wait for pecans to mature, if no other hickory trees are available.  So though thin shelled pecans may suffer heavier squirrel predation, they are less likely to have their nuts destroyed by weevils, if they grow near other species of hickory.

Pecan weevil larvae in nut

Pecan weevil larva.  Pecans mature later than hickories.  Though squirrels favor pecans over hickories, the later maturing pecans are less likely to be attacked by pecan weevils in mixed forests, giving pecans an advantage over other hickory species.

Pecans are native to river bottomland terraces where they grow in forests dominated by sycamore, sweetgum, and elm.  Other subdominants in these terrace forests include water oak, box elder, silver maple, cottonwood, green ash, hackberry, and other hickory trees. Pawpaw, bamboo cane, pokeweed, grape vine, poison ivy, and green brier make up the thick undergrowth of bottomland forests.

Pecans hybridize with 5 other species of hickory.  The nuts produced by wild pecans and hybrids vary in quality.  Most are smaller and have somewhat thicker shells than cultivated varieties of pecans, and some even have high amounts of bitter tannins–all part of their ongoing evolutionary war with squirrels and weevils.  Human cultivation of pecans on a large scale began circa 1900.  Though Georgia isn’t part of the pecan’s native range, the state is the leading producer, and there is a large demand in China and India, resulting in high prices at the grocery store for the nuts.

Most cultivated varieties of pecans don’t mature before the first killing frost occurs in Midwestern states.  A few small early maturing varieties can produce in the Midwest as can the hican–an hybrid cross between pecan and shellbark hickory.

Hican 5-nut sample prior to cracking. US quarters shown for size comparison.

 

 

 

 

 

 

 

 

 

 

 

Hican nuts–an hybrid cross between a pecan and a hickory.  They produce earlier maturing nuts  for northern locations that have frosts before pecans can fully develop.

The southern Mississippi River Valley has long served as a refuge for pecans and other hickory trees during glacial expansion cycles.  Here, they grew in mixed Ice Age forests with spruce, beech, walnut, and oak.  Pecans expanded their range north up the Mississippi River Valley following the end of the last Ice Age.

The oldest written recipe for pecan pie dates to 1886.  It was a custard pie made with sugar, eggs, and butter.  (Sugar/custard pies originated during the Middle Ages.)  Pecan pies became more popular in the 1930s when some unnamed employee of Karo syrup invented a recipe for a pecan pie using syrup as well as sugar.  I prefer my pecan pie made with maple-flavored corn syrup.

Pecan Pie

Pecan pie with whiskey maple cream sauce.  I like my pecan pies made with maple flavored corn syrup.

 

The Ecology and Evolution of Live Oaks (Quercus subsection virentes sp.)

September 2, 2016

The southern live oak (Quercus virginiana) is my favorite species of tree.  I love the sprawling canopy, usually covered in silvery-gray Spanish moss, and the way they grow in shady groves that cool off their native habitat–the hot sea islands and lowlands of southeastern North America.  The southern live oak is specially adapted to grow on the edge of maritime forests where their sturdy limbs can reach over adjacent fresh or saltwater marshes.  Before Europeans modified the environment, most live oaks occurred on the edges of watery habitats.  Unless a natural gap occurred within the forest, the limbs of most individual trees sprawled in one direction over water, enabling them to capture sunlight that other species of trees couldn’t reach.  But man cleared the original maritime forests and replanted live oaks in groves where the limbs of widely spaced trees could sprawl in all directions.  The limbs evolved to withstand strong sea winds, and when Europeans first colonized the region they were quick to make use of the solid wood for ship-building.  Today, the tree is planted as an ornamental, and its abundant acorn production feeds wild hog, deer, squirrel, and other wildlife.

There are 7 species of live oaks including the southern, the sand (Q. geminata), the dwarf or runner (Q. minima), the Cuban (Q. sagraeana), the Texas (Q. fusiformis), the Baja (Q. bradegeei), and the encina or Central American (Q. oleoides).  All of these species grow at low elevations in well drained soils.  They are evergreen trees that require cross pollination.  Live oaks will occasionally hybridize with other species of white oaks and with other species of live oaks in ranges where they overlap.  The genetic evidence suggests white oaks first evolved 28 million years ago, and the live oak group (a subsection within the white oak family) diverged from other white oaks 11 million years ago.

The Seven Sisters live oak in Mandeville, Louisiana is the largest and oldest known live oak in the world. It is estimated to be 1500 years old.

Sand Live Oak (Quercus geminata) in a stand of open pine savannah.  It is more fire tolerant than Quercus virginiana.

Dwarf Live Oak shown as a small group growing and expanding naturally via underground stems/roots

Dwarf live oak (Q. minima).  This species is fire dependent.  Its root system is much larger than the shrub itself.

The ranges of southern, sand, and dwarf live oak overlap; but they don’t hybridize often because they flower at different times and they prefer different habitats.  The southern live oak is a large tree that is fire intolerant.  This species can only grow successfully in environments where it is protected from fire such as islands surrounded by salt marsh and inlets or hardwood hammocks surrounded by swamp.  The sand live oak is fire tolerant, and it can grow in pine savannahs subject to frequent fire.  The runner live oak is a small shrub that is fire dependent.  It has an extensive root system underground and will re-sprout after a ground fire, but it can’t grow in shade.

Scientists believe live oaks evolved in southern North America because most species are frost tolerant.  The encina or Central American live oak lost this frost tolerance after it colonized the tropics.  The genetic evidence suggests the Cuban live oak is derived from the Central American species, but scientists don’t know how the ancestor of the Cuban species made it to the island.  Acorns likely rafted across the Caribbean protected from the salt water in a clump of vegetation.

The genetic evidence suggests the ancestor of the Baja live oak was formerly much more abundant, but the opening of the Sea of Cortez isolated this species.  It shared a common ancestor with the closely related Texas live oak.

Reference:

Cavender-Bares, J.; et. al.

“Phylogeny and Biogeography of the American Live Oaks (Quercus subsection virentes); a Genomic and Population Genetics Approach”

Molecular Ecology 24 2015

 

 

Apple Pollinating Bees and Rare Varieties of Southern Apples

March 3, 2016

Alarmist reports from the sensationalist media, suggesting an eventual end to the availability of fruits and vegetables because of colony collapse disorder, are completely unfounded. (See: https://markgelbart.wordpress.com/2015/06/12/pleistocene-pollinators ) In North America the honeybee (Apis mellifera) is a non-native invasive species.  The decline of this species due to this mysterious disorder may cause high honey prices, but it will not impact the pollination of most agricultural crops.  Honeybees are just 1 of thousands of pollinating insect species. A recent study of bees in north Georgia apple orchards found that honeybees comprised just 7% of the total number of bees captured.  Moreover, native bees are much more efficient pollinators than honeybees.

Researchers surveyed bees in 4 orchards in north Georgia: Mercier Orchard with 150,000 trees planted on 200 acres, Hillside Orchard with 40,000 trees, Tiger Mountain Orchard with over 1000 trees, and Mountain View Orchard with just under 1000 trees.  The scientists captured a total of 2025 bees consisting of 128 species and 30 genera.  The most common species of bee caught in their traps was the hawthorn adrena (Adrena crataegi).  It comprised 31% of the bees in the survey.  It’s named after the hawthorn bush, a common species inhabiting open woods that produces a small apple-like fruit.  This species of bee readily adapted to pollinating apple blossoms after Europeans introduced the fruit to America.  Hawthorns are in the same family as apples.  The 2nd and 3rd most common bees caught in the traps were the wasp-like bees–Lasioglossum (dialectus) imitatum and L. (d.) pilosum.  Bee families in order of abundance were the Andrenidae (mining bees) composing 46.5%, the Halictidae (sweat bees) composing 34.2%, the Apidae (honeybees and bumblebees) composing 17.1%, the Megachilidae (mason and leafcutter bees) composing 1.8%, and Collectidae (polyester bees) composing .4%.  Incidentally, the authors of this study, even with outside help, couldn’t identify 10% of the species they trapped.  There are still many species of insects in North America yet to be described and named by entomologists.  All these species of bees pollinate a wide range of native and non-native plants.

Most of the species of bees in the Andrenidae family are solitary, but the hawthorn adrena does nest communally.  The authors of this study suggest the hawthorn adrena as a replacement for honeybees in areas where the latter have suffered severe population declines.

Andrena? - Andrena crataegi

Adrena crataegi is by far the most abundant species of bee that pollinates apples in North Georgia.  It’s native to North America and could be used to replace honeybees used for pollinating fruit.

Lasioglossum imitatum

The wasp-like bee (Lasioglossum imitatum) is the 2nd most common pollinating bee in north Georgia apple orchards.

European settlers planted apple trees in North America as soon as they arrived on the continent.  Apples were most important for the production of hard cider, a substitute for beer in regions where barley crops were unreliable.  Alcoholic beverages were considered an essential part of daily living during the colonial era.  Some rich planters imported young trees bearing the highest quality fruit known in Europe, but most settlers started their orchards from seeds they obtained at little expense.  Apple trees grown from seeds don’t produce the same quality fruit as their parent.  Most fruit from seedling apple trees is of poor quality.  Twigs from the rare tree that does produce good fruit are grafted on root stocks of other apple trees.  That is how good varieties of apples are cultivated.

Settlers moved inland and planted large orchards from apple seeds.  The majority of these trees produced fruit that was used to fatten hogs but served no other purpose.  A few trees produced fruit that was good enough to feed members of the household.  A few mature apple trees would provide plenty of fruit, even for the large farm families of the time.  Other apple trees produced fruit with certain qualities particularly suited for certain purposes.  Some trees produced apples that more readily fermented into cider and vinegar.  Some of the best cider apples were considered unpalatable fresh off the tree but made a superior drink when fermented.  Other trees bore apples that were only of fair eating but kept without refrigeration until late spring.  Still others bore palatable fruit as early as June.  A farm with a long-keeping variety and an early bearer could have a year round supply of apples.

Carolina Red June Fruit

Most apples ripen from August-October, but the red June apple is prized for ripening earlier.

 

The horse apple was one of the most popular apples in the south before 1930.  Not great for fresh-eating, the vigorous trees reportedly produce large crops of apples that are good for cider, drying, and jelly.

George Washington and Thomas Jefferson grew Hewe’s crabapple for cider.

Johnson Keeper apples originated in Mississippi some time before 1885.  They keep until late spring without refrigeration.

The Mattamuskeet apple is a very rare apple originating near Lake Mattamuskeet, North Carolina. It’s known for its long-keeping quality.  Some claimed this apple could keep for years without refrigeration.  This variety has an interesting origin story that may or may not be true.  Supposedly, an Indian found the seed of this apple in the gizzard of a goose he shot along the shores of Lake Mattamuskeet.  He planted this seed and gave the twigs (scions) to European settlers.

Some of these antique apple varieties were better suited for drying and could be kept indefinitely.  Varieties that disintegrated in stews to add a tart sweet flavor increased the repertoire of country cooks.  Using apples to season pioneer stews of wild game precedes the common use now of tomatoes in stew.

Over 1800 varieties of apples were grown in southern orchards between 1600-1930.  The most successful varieties were well adapted to the southern climate with its long humid summers and mild winters.  Apples require a certain amount of cold weather or they won’t bear well.  Many varieties grown in the south had a low chilling requirement.  They were also resistant to local diseases.  Many of these old-timey varieties became rare or even extinct when family farmers left the land to take factory jobs during the middle of the 20th century.

Fewer than 20 varieties of apples are sold in grocery stores today.  These very sweet, all purpose apples probably do taste better than most of the antique varieties but lack the characteristics that made the older types better for certain purposes such as the making of apple butter, jelly, or cider. In recent years 2 major brands of hard cider have begun to appear on the beer aisle in grocery stores.  They both taste like yeasty bad home brew.  The makers of these brands might want to experiment with some of the older varieties of cider apples, so they can improve their product.

References:

Calhoun, Creighton

Old Southern Apples: A Comprehensive History and Description for Collectors, Growers, and Fruit Enthusiasts

Chelsea Green Publishing 2010

Schlueter, Mark; and Nicholas Stewart

“Native Bee (Hymenoptera: Apoidea) Abundance and Diversity in North Georgia Apple Orchards throughout the 2010 Growing Season (March to October)”

Southeastern Naturalist 14 (4) 2015

 

 

Wild Squash (Cucurbita sp.) was Abundant during the Pleistocene

November 30, 2015

A new study suggests wild squash and megafauna had a long mutually beneficial relationship during the Pleistocene.  Wild squash evolved bitter poisons known as cucurbitains in their flesh that discouraged seed consumption by rodents.  However, large mammals have fewer bitter taste receptors and can consume large quantities of cucurbitains without ill effect.  Most squash seeds could survive passage through the gut tract of a megaherbivore and were spread throughout the environment in fertile piles of dung.  The squash plants thrived in open sunny environments created by megafauna foraging and trampling.  Mammoths, mastodons, and giant ground sloths killed trees by uprooting them or by stripping off the bark.  This opened woodland canopies where squash plants were exposed to direct sunlight.  Trampling and wallowing also killed grass, resulting in bare soil environments where squash plants could germinate with less competition.  In exchange for providing food, wild squash enjoyed a wide and continuous geographic distribution during the Pleistocene along megafauna game trails, around water sources, or wherever megaherbivores congregated.

Wild squash seeds retrieved from the droppings of mastodons. (Image: Lee Newsom / Penn State)

Wild squash seeds extracted from ancient mastodon dung.

After the megafauna became extinct the range of wild squash was fragmented into relic habitats.  Some species likely became extinct.  Seeds found in fossil mastodon dung in Florida don’t exactly match those of any known species.  However, humans began cultivating squash about the same time the megafauna died out (circa 10,000 BP). Initially, humans used the squash rinds as containers, but the seeds could be eaten as well, if the toxic pulp was washed off the edible kernels.  Humans selected for mutated squash that had sweet rather than bitter flesh.  Successful cultivation of improved varieties didn’t occur until wild squash became less common in the natural environment because when improved varieties backcross with wild varieties, a bitter hybrid is produced.  This suggests good varieties of squash were not cultivated until Pleistocene megaherbivores were completely gone or rare.  Without mastodons wild squash lost their distributors, and cultivated squash could grow with less chance of backcrossing.

The scientists who conducted this study looked at the genomes of 91 squash specimens consisting of 12 species and including 42 domesticated specimens, 30 wild specimens, and 19 specimens found at ancient archaeological sites.  They determined squash was domesticated independently in several different regions in Mexico and southeastern North America.  The genetic evidence suggests the Okeechobee gourd (C. okeechobeensis), today restricted to 2 regions of Florida, is essentially the same species a C. lundelliana, a wild squash found in Mexico.  The Okeechobee gourd likely had a more continuous distribution during the Pleistocene.

They also looked at the genomes of 46 species of mammals to analyze the bitter taste receptors of each.  Smaller mammals and humans have many more bitter taste receptors than elephants or rhinos.  Smaller mammals are more vulnerable to toxins and need to avoid them.  Large mammals have greater tolerance to toxins because of their physiology and size.

See also:

https://markgelbart.wordpress.com/2014/09/28/mastodons-ate-wild-squash/

Reference:

Kistler, L., et. al.

“Gourds and Squash (Cucurbita sp.) Adapted to Megafaunal Extinction and Ecological Anachronism through Domestication”

PNAS November 2015

 

Pleistocene Sweet Potatoes (Ipomoea batatas)

November 24, 2015

Thanksgiving wouldn’t be complete without sweet potatoes and mashed Irish potatoes (Solanum tuberosum).  Both species originated in Central and South America, and paleo-indians were the first humans to eat them, possibly as early as 13,000 years ago.  Genetic and morphological studies suggest the sweet potato originated in the region located between the Yucatan Peninsula, Mexico and Venezuela.  The ancestor of the sweet potato is not known in the wild and may be extinct.  The modern sweet potato is likely a hybrid cross between this extinct wild ancestor and a species of morning glory (Ipomoea triloba).  Foraging humans may have gathered the sweet potato’s wild ancestor to extinction.  The oldest archaeological remnants of sweet potatoes were found in a Chilca Canyon cave.  Chilca Canyon is located near the south central Pacific coast of Peru, and it was much farther inland 10,000 years ago when paleo-indians left remains of their food here.  (At least 1 archaeologist disputes the age of this evidence.)  This region was a coastal savannah with some wooded areas then.  Remains of other species found in this cave in addition to sweet potato include Irish potato, olluca (Ullucus tuberosa), jicama (Pachyrhizos crosus), bottle gourd, and prickly pear.

Archeologists believe paleo-indians initially spread sweet potatoes and other edible plant species by accident.  All of the above mentioned plants will readily sprout from their tubers, roots, or seeds, if carelessly tossed in a garbage pile in contact with soil. By observing these accidents, paleo-indians learned to deliberately plant and care for these valuable plants when climatic conditions deteriorated and food became scarce.  Climate did become more arid along the Peruvian coast during the Holocene.  Native Americans settled near oasises located in a landscape that had transformed from savannah to desert.  Several archaeological sites in the Pampas de las Llamas region show that by 3500 BP native Americans were cultivating sweet potatoes, Irish potatoes, common bean, lima bean, oca (Oxalis tuberosa), oculla, peanuts, peppers, turban squash, avocado, edible canna (Canna edulis), cotton, bottle gourd, eggfruit (Pouteria lucuma), peanut butter fruit (Buchosia armeniaca), and manioc root.  The remains of wild game, marine mammals, and fish were also found at these sites.

Manioc root is poisonous, if not processed in a certain way.  When paleo-indians first colonized South America, they were unfamiliar with the many plants that grow in tropical climates.  The popular image of paleo-indians as meat-eaters is partially true, but an healthy human diet includes carbohydrates.  Surely, paleo-indians were aware that many plants were poisonous, yet the craving for carbohydrates drove them to take chances with unfamiliar roots, tubers, and fruits.  This trial and error likely led to many deaths or at the very least bad stomach aches.  But poisonous compounds are usually bitter.  This important clue helped guide the selection and processing of the unfamiliar plants.  Early people learned that some poisonous plants could be made edible by leaching the poisons in boiling water or by some other processing method.  They must have been really hungry for carbohydrates to make that much effort.  Paleo-indians got lucky when they discovered the wild ancestor of the sweet potato.  There is a species of morning glory (I. pondurata) with an edible root that ranges in southeastern North America.  Reportedly, cooks can rid the bitterness by boiling the root in several changes of water.  It’s likely the first sweet potatoes (a species of morning glory) had to be processed in the same way.  Paleo-Indians were rewarded with an extremely nutritious food.  Sweet potatoes are high in protein, carbohydrate, magnesium, potassium, sodium, phosphorus, vitamin C, B vitamins, and beta-carotene which the human body converts to vitamin A.

Thousands of years of deliberate cultivation has led to many delicious varieties of sweet potatoes that need no processing other than baking.  There are orange, yellow, white, and purple sweet potatoes.

Different varieties of sweet potatoes.

Scientists think the sweet potato is the result of a cross between this species of morning glory and another unknown ancestral species in the ipomoea genus.  Humans crossed them either accidentally or deliberately.

Ipomoea pandurata is a morning glory with an edible root that is native to southeastern North America.  The roots reportedly need quite a bit of processing to make them palatable. The seeds of I. violacca are used as an hallucinogen similar to LSD.

I like candied sweet potatoes with or without marshmallows, but I think the best way to prepare them is by simply baking them, then serving with plenty of butter and cinnamon sugar.  I use baked sweet potato flesh in pies I make with condensed sweetened milk, brown sugar, eggs, ginger, and nutmeg.  White sweet potatoes are drier but sweeter than orange sweet potatoes.  Yellow sweet potatoes were the most popular variety in the U.S. during the 1930’s but have since fallen from favor and are hard to find, yet they taste as good as the orange ones.

Sweet potatoes grown in Louisiana and Mississippi are marketed as “yams” but they are not true yams–a root rarely found in the supermarket.  True yams are not closely related to sweet potatoes but belong to the dioscorea genus.

Canna flaccida

Canna flaccida. The roots of the canna lily have also been eaten in Peru for thousands of years, probably since the Pleistocene.

Ollucos

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The remains of olluco (Ullucus tuberosus), another edible species  found in the Chilca Canyon caverns, date to possibly 10,000 BP.

References:

Ugent, Donald; and Lande Peterson

“Archaeological Remains of Potato and Sweet Potato in Perus”

International Potato Center 1988

Zhang, D.P.; et. al.

“AFCP Assessment of Sweet Potato Genetic Diversity in 4 Tropical American Regions”

International Potato Center 1997-1998

Pleistocene Apples (Malus sp.)

August 26, 2015

The ancestor of all domesticated apples (Malus domestica) still grows in montane forests located in Kazkhstan, Kyrgyztan, and western China.  A genetic study shows that all modern cultivated apples descend from Malus sieversii, a species that reaches 60 feet in height and grows among pine and oak trees as a co-dominant.  Traders brought seeds of M. sieversii to Europe where it readily crossed with the European crabapple, M. sylvestris.

Image

The mountains of Kazakhstan are where the ancestors of modern apples grow wild.

Photo of apples hanging from a tree.

Malus sieversii, 1 of the ancestors of the domesticated apple (Malus domestica).

Scientists believe the first apple trees evolved 10 million years ago and originally were a small sour fruit spread by defecating birds.  Elephants and bears favored larger sweeter mutations of this fruit, and they helped shape the evolution of a food that was more palatable to humans by also spreading the seeds in their dung.  Humans began cultivating apples 4000 years ago, and there are 3000 known varieties.  Just .03% of these varieties equals 70% of the world’s production.

There are an estimated 30-55 species of apples and crabapples in the Malus genus.  Scientists disagree over species status of some populations, and the propensity of species in this genus to crossbreed adds to the confusion.  Some species of crabapples are native to North America.  Mastodon dung excavated from the Aucilla River in Florida contained some crabapple.  None of America’s native crabapples, however, are comparable in quality to M. sieversii.  American crabapples rarely become a co-dominant tree like M. sieversii does in the mountains of southwest Asia.  Instead, they grow as an occasional tree in early stages of forest succession.

Apple trees descended from orchards planted by Europeans do occur throughout North America.  Circa 1974, I saw an apple tree that produced good quality green apples in an oak-dominated woods in Niles, Ohio.  The quality of most wild apples growing from seed reportedly varies.  Euell Gibbons wrote that most are not worth cultivating for fresh eating, but they do make good cooking apples.  All apples sold in grocery stores are the progeny of rare mutations.  Horticulturalists graft branches of the high quality mutations (known as scions) on rootstocks of uncultivated apple trees.  Trees are available with as many as 5 different varieties grafted on to them, but they are expensive.  Think hard before buying one of these 5 on 1 trees–insect pest can kill the tree thereby wasting money.

The Odd Disjunct Range of the Sand Myrtle (Kalmia buxifolia)

January 25, 2015

Organisms with disjunct range distributions fascinate me because they provide clues about past natural environments.  Direct evidence of past landscapes is rare–over 99% of potential fossil evidence has vanished without being preserved in any way.  The existence of extant species with odd distributions helps fill in gaps in our knowledge of natural history, though it requires some uncertain speculation. The sand myrtle is 1 of many species with an interesting disjunct  range distribution.  This member of the heath family (rhododendrons and blueberries) is found in the sandhills of southern New Jersey; the mountains of northeastern Georgia, eastern Tennessee, and western North Carolina; the sandhills of North Carolina’s coastal plain, and some isolated monadnocks in the upper South Carolina piedmont.

Caesar’s Head State Park in South Carolina.  Sand myrtles grow on isolated rocky hills such as this.

Sand Myrtle (Kalmia buxifolia) at Garden Supply Company

A sand myrtle in full bloom.  They are a short plant, growing to just 20 inches in height.  They can’t grow under tree canopies.

Range map of Kalmia buxifolia shaded in  light green.  The populations are more isolated than this map indicates.

One is left to wonder why the sand myrtle disappeared from or doesn’t occur in the areas between its disjunct populations.  One hypothesis could be that it reached suitable habitat through seed transport via bird droppings.  But the great distances between disjunct populations precludes this possibility.  The seeds, if they even stayed viable within the bird’s digestive system, would be excreted long before they reached the other territories.  Wind distribution is a more viable hypothesis.  Winds carry insects, pollen, and light seeds great distances, and this light organic material eventually settles.  Still, this seems an unlikely explanation because sand myrtle should occasionally be found growing in areas between their current distribution, even if the habitat is unsuitable.  The most likely hypothesis requires a bit more complicated explanation.  Sand myrtle may have existed throughout the entire region during the dry climatic phase of the late Pliocene/early Pleistocene.  Today, sand myrtle favors open sunny conditions on poor rocky or sandy soils.  Arid grasslands expanded when dry climates prevailed in the south.  These dry prairie and scrub habitats were subjected to overgrazing by herds of megafauna, leading to bare soils, especially during droughts.  Windy conditions stripped the top soil.  Sand myrtle was able to grow on these poor soils with little competition from trees.  When climatic conditions changed to a wetter cycle, deciduous forests expanded and outcompeted sand myrtle by shading them.  Grassy savannahs were also unsuitable now because frequent lightning strikes led to more fires.  Sand myrtle is both fire and shade intolerant and can only survive in communities with poor shallow soils where fire is infrequent. This probably explains why sand myrtle is currently found in rocky mountains and sand hills and nowhere else.

A Note on my Cod Liver Experiment

In my last blog entry I reported my visit to the Buford Highway Farmer’s Market.  One of the products I purchased was cod liver in a can.  I had a chance to try it yesterday.  When I opened the can, I was surprised to find that most of the volume was filled with oil rendered down from cooking the liver in the can.  I removed over half of the liver and squirted lemon juice on it.  The first bites tasted like canned tuna, and maybe a little like oysters.  But the texture was very soft.  I started having a hard time accepting such a soft texture, so I ate the rest of this portion on buttered toast.  This soft texture was not unlike that of scrambled eggs.  I’m used to eating scrambled eggs, but I usually put lots of shredded cheddar cheese and smoked chipotle pepper in my eggs, and I also put them on buttered toast.  Even with these additions, I still prefer eating my scrambled eggs with either salsa or brown mushroom gravy.  Eggs are just so bland by themselves.  I debated with myself whether to eat the rest of the cod liver for lunch today, but last night I fed it to the cat.  Instead, I’m going to have a nice salami sandwich.

Southeastern Grasslands are of Great Antiquity

May 29, 2014

I enjoy watching a summer thunderstorm.  Lightning strikes offer a natural fireworks show that sometimes surpasses the manmade kind.  The furious wind and roaring thunder show the excited side of mother nature.  It’s the dangerous side of nature–a human could be vacuumed into the sky by a tornado, electrocuted by lightning, or clobbered by a hailstone or wind-strewn debris.  Nobody, not a king nor a baby, is immune to these hazards.

Natural fireworks.

Some anthropologists and a few old school ecologists wrongly believe most of the grasslands that occurred in southeastern North America when Columbus accidentally sailed into the Caribbean were the result of manmade fires.  Reed Noss dispels this notion in his book, Forgotten Grasslands of the South. The map below shows the frequency of lightning strikes in North America.  The south, and especially Florida, has more lightning strikes than any other region of the continent.  Dr. Noss believes the high frequency of lightning strikes can spark enough wild fires to maintain abundant grasslands without any human activity.

Map of average annual lighting strikes in North America between 1989-1999.  Lighting strikes were naturally common enough to have sparked grassland-creating wild fires long before humans arrived in North America.

Long Distance Controlled Burn

A longleaf pine savannah on fire.  Longleaf pines are one of the few species of tree whose seedlings can survive fire.

Several lines of evidence support Dr. Noss’s conclusion that anthropogenic activity was not necessary to maintain grasslands.  Formerly, longleaf pine savannah covered most of the coastal plain region of the south.  There were even patches of pine savannah in the piedmont region, though oak and hickory dominated that area.  There are over 900 species of plants endemic (meaning they live nowhere else) to longleaf pine savannah compared to just 80 endemic species found on the grasslands of the Great Plains.  A high number of endemic species suggests an ecosystem of great antiquity and stability.  Because evolution is usually a slow process, it’s not likely that all of these endemic fire-dependent species could have evolved in just the last 12,000 years.  Longleaf pines require fire intervals of 1-10 years or hardwoods will crowd them out.  Longleaf pines grow slowly, taking decades to reach reproductive age.  A species that reproduces this slowly would have never been able to adapt quickly enough to survive a sudden change in fire regime caused by man.  These fire dependent species must have already been present before man colonized the region.

Many species of animals are also endemic to pine savannahs.  The gopher tortoise and the red cockaded woodpecker are perhaps the 2 most well known vertebrates dependent on this fire-influenced environment. Gopher tortoise fossils have been found that date to millions of years ago, while red cockaded woodpecker fossils come from deposits in the vicinity of 200,000 years old.  The presence of these species and many others in the fossil record long predate man’s entrance into the region.  This is obvious evidence that southern grasslands preceded man.

There was a lower frequency of lightning strikes during the coldest stages of the Ice Ages.  Evidence from most fossil sedimentary sites show little, if any charcoal, indicating reduced fire activity.  However, less precipitation combined with megafaunal grazing created grasslands during the colder climatic phases.  Following the megafaunal extinctions, fire activity spiked because so much vegetation was no longer being eaten and instead it became dry tinder.

During the Last Glacial Maximum, longleaf pine savannahs still occurred in refugium located in Florida, Louisiana, Texas, and probably along the continental shelf where sea levels regressed.  Paradoxically, these areas were warmer and wetter during Ice Ages because the Gulf Stream shut down and warm water that normally circulated north pooled around these lower latitudes.  Oak scrub and prairie, the result of aridity and megafauna foraging, predominated in the upper coastal plain.  Longleaf pine savannah didn’t recolonize the upper coastal plain until about 6,000 years ago, but the pollen record suggests this type of environment has waxed and waned cyclically for millions of years, becoming common and widespread during warm and wet climatic phases.

The Corn Field Weed

November 25, 2013

Our favorite Thanksgiving foods are all of North American origin.  Turkey, potatoes, sweet potatoes, pumpkins, most varieties of green beans, and cranberries were unknown in Europe and Asia before Christopher Columbus made first contact with Native Americans.  Without the contribution of Native American agriculture our culinary repertoire would be destitute, also lacking corn, chocolate, vanilla, peppers, and perhaps most importantly, tomatoes.  Tomatoes originate from a plant that grows wild in South America–Solanum peruvianum.  It grows at mid-elevations where the climate is not too cold nor too hot.  Unlike its cultivated descendent–Solanum lycopersicum–the wild tomato is resistant to disease and insect infestation.  Some individual plants even exude a sticky substance on their leaves that traps insects and stops them from defoliating the plant.

Ripe wild tomatoes.  Some varieties of modern cultivated tomatoes are green when ripe.  A green color in ripe tomatoes is considered a primitive trait.

Carter and Eli 001

I harvested these Cherokee purple tomatoes late last June from my garden.  They are an heirloom variety, meaning they produce true to seed.  Most tomatoes sold in grocery stores are hybrids.  Despite garden catalogue propaganda, heirloom varieties are no better tasting than hybrids.  I also grew Better Boy hybrids, and they  tasted better.  In previous years the Cherokee purple tomatoes tasted better than the Better Boys.  The variation in flavor is influenced by soil nutrients, sunlight, and weather as much as by variety.

Native Americans probably first found wild tomatoes growing as weeds in their corn fields.  Good quality fruits were seasonal and rare in this region then, explaining why the early Peruvians would make a trial of eating these sour and bitter fruits.  Occasionally, they found individual plants that produced more palatable fruits, and the seeds of these were saved and planted on purpose.  About 2500 BP the Peruvian Native Americans colonized or conquered Mexico and carried seeds of this plant with them.  This is where cultivation led to the development of what we would recognize as a modern tomato.

A variety of heirloom tomatoes–all descended from the species of small green wild tomato pictured above.

Horticulturalists still use wild tomatoes for crossbreeding with cultivated tomatoes to help strengthen disease and insect resistance.  As every backyard gardener and truck farmer knows, tomatoes are inbred weaklings, susceptible to disease.  Almost every tomato plant I’ve ever grown eventually develops some sort of blight.  Horticulturalists hope to combine disease resistance of wild tomatoes with the good taste of cultivated tomatoes.

Tomato horn worm (Manduca quinquemaculatata).  It’s actually the larva of a large moth.  I once read an article written by an idiotic gardening advice columnist who suggested gardeners only needed to look over their gardens once a week.  A few of these hornworms can defoliate an entire row of tomato plants in about 3 days.  I check daily and crush them on sight.

The solanum genus also includes the Irish potatoes (Solanum tuberosum) and eggplants (Solanum melongena). The fruit of some other plants in the Solanidae family, such as peppers and husk tomatoes are edible, but others such as belladonna and nightshades, have poisonous leaves and fruit.  This explains why it took centuries for Europeans to develop an appetite for tomatoes.