Thursday, January 22, 2009

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.


Katrina said...

At the PCSS meeting, I won an
Eriospermum plant in the lottery, but it has not grown much. Can you tell me something about culture? Thanks.


Matt said...

Once the leaves have expanded in the autumn, they don't grow any further; the tuber underground does get larger, though. So, your plant is probably fine. Next winter's leaf should be bigger.

Katrina said...

Thanks, Matt.

MAR said...

very very nice blog.
i only cannot tell the difference between CERVICORNE and DREGEI. they both look very similar, don t they ?