Ginkgo, and the Trouble with Living Fossils

Ginkgo lined walkway at the University of Tokyo.

The Maidenhair Tree, Ginkgo biloba, is the last surviving remnant of a group of non-flowering seed plants (phylum Ginkgophyta) that way back in the Mesozoic had a worldwide distribution and were represented by multiple genera and species. Ginkgo came to the attention of European botanists in 1690, via cultivated trees in Japan, though it seems that the original home of G. biloba was the mountains of southwestern China. It is debatable whether truly wild populations of Ginkgo trees even exist anymore, but through cultivation the Ginkgophyta have regained shades of the ubiquity that they had in the age of the dinosaurs.

Ginkgo is a classic example of what are sometimes called “living fossils,” a lone hanger-on from a group that was far more diverse, widespread and ecologically important in the distant past, as revealed by the fossil record. The genus Ginkgo itself is known from the upper Triassic (200 million years ago) onward, with some fossils being quite similar, at least in form, to the modern Maidenhair Tree.

The term “living fossil” bothers me, though. Present day ginkgos aren’t identical to the fossils, and many of the ancient ginkgophytes don’t resemble the modern street tree in the slightest, unless viewed by someone with a background in paleobotany and plant morphology. The basic workings of genetics imply that it is essentially impossible for a real world population to remain genetically static from one generation to the next, let alone for millions of generations. So, Gingko biloba is certainly not a literal living fossil, untouched by the passage of time.

Even non-literal applications of “living fossil” are problematic. Ginkgos qualify as living fossils in large part simply because there weren’t that many of them around before people took them into cultivation, and they were confined to one obscure corner of eastern Eurasia. If it so happened that thousands of species of Ginkgophyta had survived into the present, and they grew in every forest, savannah, patch of desert scrub and vacant lot north of Antarctica, nobody would call them living fossils, never mind that they bore similarities to certain fossil remains.

Old Ginkgo tree at Washinomiya Shrine, Saitama, Japan. This individual has been coppiced: the original trunk was cut, and the tree is resprouting with multiple stems.

In our world, the Ginkgophyta barely squeaked by into the present, and another group of seed plants, the Magnoliophyta or flowering plants, diversified and came to dominate most terrestrial ecosystems. The designation of Ginkgo as a living fossil, and magnoliophytes—for example, petunias—as just ordinary plants, is purely retroactive and largely arbitrary: flowering plants, after all, have a fossil record that extends well back into the Mesozoic. Flowering plants share a common ancestor with Ginkgo, and the two lineages have been evolving for exactly the same amount of time since they diverged. A living fossil is more a matter of perception and lack of familiarity, than anything inherent in the plant.

In some alternate reality where pernicious ginkgophyte weeds infest suburban gardens of edible tomato-like ginkgophytes, and the only flowering plant that has dodged extinction is one species of petunia growing in a remote valley in Peru, perceptions would be different. Ginkgo biloba would be just another street tree, and petunias would be living fossils, a rare and freakish survival from a vanished world.

Reference: Gifford, E.M. & A.S. Foster. 1989. The Morphology and Evolution of Vascular Plants, Third Edition. W.H. Freeman and Co., New York.

Bald Eagles in NY

Eagles at George's Island, Montrose, NY.

On Saturday I got over to Westchester County, New York, to visit some family and friends. The afternoon's amusement was attending Eaglefest, at various sites along the Hudson River in the Croton-on-Hudson vicinity. It went over well: the weather was considerably warmer than it has been lately, and we saw plenty of juvenile and adult Bald Eagles (Haliaeetus leucocephalus), flying, perching, and at one point getting chased by a Red-tailed Hawk, which looked puny in comparison. My wildlife photography skills and equipment aren't up to National Geographic standards, but the bird-shaped blobs in the photos are eagles.

George's Island wide view. There are about 20 eagles in the trees.

Darwin's Orchid in Flower

Here at the UConn Ecology and Evolutionary Biology Greenhouses we have a special treat, just in time for Darwin Day and the 200th anniversary of Charles Darwin's birth, coming up on February 12. The specimen of Angraecum sesquipedale, commonly known as "Darwin's Orchid," is in bloom, complete with the improbably long nectar spur that lead the great biologist to predict the existence of a pollinating moth with an improbably long nectar-sucking proboscis. This particular flower has a spur about 30 cm (11.5 inches) long, for example, with nectar at the base. The pale color of the flower, and its spicy-musky scent (strongest at night) are also typical features of moth-pollinated blooms. The hypothesized moth, Xanthopan morgani ssp. praedicta, was discovered in 1903, 21 years after Darwin's death, and only quite recently has anyone actually observed the moth doing its thing in the rainforests of Madagascar.

The special genius of Darwin is evidenced here not so much by the fact that he realized that only a moth with an outsized proboscis would be attracted to an Angraecum sequipedale flower--any clever naturalist with a basic knowledge of pollination biology could have intuited the characteristics of the sort of critter that would be needed to pollinate such a bloom--but in that he provided a clear explanation for the history and peculiar details of the Angraecum story. Here's the man himself:

If the Angræcum in its native forests secretes more nectar than did the vigorous plants sent me by Mr. Bateman, so that the nectary becomes filled, small moths might obtain their share, but they would not benefit the plant. The pollinia would not be withdrawn until some huge moth, with a wonderfully long proboscis, tried to drain the last drop. If such great moths were to become extinct in Madagascar, assuredly the Angræcum would become extinct. On the other hand, as the nectar, at least in the lower part of the nectary, is stored safe from depredation by other insects, the extinction of the Angræcum would probably be a serious loss to these moths. We can thus partially understand how the astonishing length of the nectary may have been acquired by successive modifications. As certain moths of Madagascar became larger through natural selection in relation to their general conditions of life, either in the larval or mature state, or as the proboscis alone was lengthened to obtain honey from the Angræcum and other deep tubular flowers, those individual plants of the Angræcum which had the longest nectaries (and the nectary varies much in length in some Orchids), and which, consequently, compelled the moths to insert their probosces up to the very base, would be fertilised. These plants would yield most seed, and the seedlings would generally inherit longer nectaries; and so it would be in successive generations of the plant and moth. Thus it would appear that there has been a race in gaining length between the nectary of the Angræcum and the proboscis of certain moths; but the Angræcum has triumphed, for it flourishes and abounds in the forests of Madagascar, and still troubles each moth to insert its proboscis as far as possible in order to drain the last drop of nectar.

Darwin, C. R. 1862. On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. pp. 201-203. London: John Murray. [Darwin Online link]

The orchid is not providing nectar out of some vegetable sense of charity, it is making the moth struggle for every drop and still holding a little more just out of reach, maximizing the chances that the moth will get stuck with pollinia (specialized adhesive pollen bodies) to carry to the stigma of the next Angraecum flower. The average nectar spur is a bit longer than the average proboscis. The moth, for its part, just wants a meal, and may in fact be actively trying to avoid getting a package of orchid pollen glued to its mouth parts, but is forced to cram its head all the way into the flower by the lure of the nectar at the bottom of that overly long spur.

The seemingly absurd length of nectar spur and moth proboscis is the outcome of an evolutionary arms race. Moths with slightly longer proboscises got more nectar, and prospered. Orchids with slightly longer spurs were more effective at foisting pollen onto moths and getting moths to deposit pollen onto their stigmas. Any angraecums with spurs shorter than a moth proboscis were unable to force the moths into the proper position to pick up or drop off pollen, and would have found themselves on the wrong end of the process of natural selection. The arms race may very well be ongoing to this day, unless one or other of the combatants has come up against structural limitations to the length of tube it can support.

A. sequipedale is on display in the EEB greenhouses for as long as the flower holds up (probably a week or so), and anyone who's in the area is welcome to stop in and see it in person.

Eriospermum cervicorne

Eriospermum cervicorne plants in January (about 3 inches/8cm tall).

The New England woods may be icy and silent this time of year, but inside of the greenhouse the South African winter bulbs are green and active. South Africa is home to the most diverse flora of geophytes—bulbs, tubers and other plants that survive unfavorable conditions as underground storage organs—in the world, and many of these come from the winter-rainfall zone in the southern and western parts of the country. Winter geophytes have adapted to grow in the temperate, rainy winter months, and then hunker down for a long dormancy in the dry summer heat.

Eriospermum cervicorne (“deer antlers with hairy seeds,” more or less) is a tuberous plant found in sandy soil on granitic hills in central Namaqualand, in western South Africa. In late summer the tubers, which look like smallish russet potatoes, send up racemes of white flowers. Only after the flowers are finished and seed is set, in autumn, do the leaves appear. As with many Eriospermum species, the flowers of E. cervicorne are fairly bland, while the foliage is distinctive and memorable.

The leaves of E. cervicorne are borne singly, one per tuber, and are dominated by a mop of antler-like outgrowths called enations. Enations are green emergences from the upper surface of the leaf, which increase the plant’s light-catching photosynthetic area (important for plants trying to intercept weak winter sun, even in sunny southern Africa), while being more resistant to wind damage than just a larger flat leaf.

Enations seem to be an evolutionary alternative to dissected leaves (sometimes termed compound leaves), in a genus where the pattern of leaf development precludes the growth of ordinary dissected leaves. Eriospermums are monocots, like lilies or grasses, and have leaves that expand from a basal zone of cell division. Therefore, they cannot develop complex dissected leaves, like those in ferns, through the action of growing points along the leaf margin. Enations can be thought of as an unorthodox method of producing a shrubby, wind-resistant photosynthetic surface, in a group of plants with developmental constraints that rule out the usual sorts of finely divided leaves.

Like most South African geophytes, E. cervicorne appreciates cool nights (anything short of frost is fine) and warm days this time of year. Soil moisture is important for proper growth in the cool season: the plants should never dry out completely, but shouldn’t stay soggy, either. The limiting factor for northerners trying to cultivate winter-active desert plants like E. cervicorne is likely to be sunlight; the plants will soak up as many hours of direct sun as can be provided. During the dormant period, from April to August or so, Eriospermum pots can be left in a sheltered corner out of the rain and neglected.

Japan Trip

Tougudou hall, on the grounds of Ginkakuji (the Silver Pavilion) in Kyoto: my current desktop image.

People occasionally somehow get the idea that I’m an enthusiastic and frequent traveler, but that’s pretty far from the truth. I stick close to home most of the time, though every once in a long while I scrape together enough money and enthusiasm to do something big, like my vacation in Japan this October.

I went over with a couple of friends from Connecticut, which was great for defraying costs and providing moral support. We planned out our own itinerary, which also cut expenses, in addition to providing the freedom to go where we wanted at our own pace. It worked out well, though it certainly helped that we all knew some Japanese, and had some friends over there.

I traveled in the southern part of the main island of Japan, in the Tokyo and Kyoto regions. This area has a humid subtropical climate, somewhat similar to the coastal Carolinas and Georgia, and October is considered a good time to visit: not stifling, but not frosty, either. Apparently, this October was unusually hot and hazy, and the weather was more summer-like than I had expected. It wasn’t unpleasant, but I quickly went through my supply of short-sleeved shirts.

Tokyo’s “electric town,” Akihabara. Across the street are a crane-game arcade, and infamous amateur comic shop Tora no Ana (The Tiger's Den).

Tokyo is a little overwhelming. It’s one of the largest cities in the world, with close to 13 million residents, and the urban landscape stretches out to the horizon in every direction when viewed from the top of the skyscrapers in Shinjuku (you can take the elevator up the Tokyo Metropolitan Building for free). But it isn’t too hard to get around; the train system is user friendly, and important signs usually give English translations.

Echeverias and a Peanut Cactus (Chamaecereus silvestrii) along a street in Tokyo.

Home base was a traditional inn (or ryokan) called Homeikan, close to the University of Tokyo, in a quiet residential neighborhood. I quickly felt comfortable in the area, which wasn’t nearly as hectic as the central parts of the city. There wasn’t much space for horticulture, but the inn had a small but immaculately maintained traditional garden. Around the neighborhood, people had collections of potted plants wherever they could find space, and I even spotted some aloes, echeverias and mesembs. The climate is warm enough that what would be houseplants in Connecticut stay outside year round. On plots of open ground around street trees near the inn someone had even planted Brugmansia (Angel’s Trumpet), which I usually think of as a true tropical plant.

Matt at Nandaimon, a gate near Todaiji, Nara Park

I also visited Kyoto and Nara, both former capitals of Japan that are famous for their ancient shrines, temples and gardens. Some of the most beautiful scenery, I thought, was at Ginkakuji, the Silver Pavilion, at the base of the mountains on the eastern side of Kyoto. Moss gardening is a specialty at the Silver Pavilion, and there was even a display showing which mosses were considered weeds, and which were carefully nurtured. Nara was wonderful as well, with a central park that includes numerous historic sites, including Todaiji, a Buddhist temple that is the largest wooden structure in the world. Nara Park is also home to a large number of more or less tame deer, which have the run of the place and will follow visitors around looking for handouts.

Hill east of Ginkakuji, mid-October, with maple foliage (Acer palmatum) starting to change color.

All in all, I had a fantastic time during my two weeks in Nippon. I would love to go back sometime to explore more in Tokyo, Kyoto and Nara, and maybe try to get further afield. Until then, I'm slowly putting together a longer and nerdier chronicle of the trip at my Japanese 2-D culture blog, Moetic Justice.