Tuesday, August 25, 2009
Welwitschia mirabilis is a gymnosperm (cone bearing, non-flowering seed plant) endemic to the Namib Desert in southwestern Africa. Welwitschia is in a category of its own in the plant kingdom, morphologically speaking: seedlings produce exactly two foliage leaves before the shoot apex aborts. The resulting stubby trunk with pair of strap-like leaves can live for centuries, gradually expanding by growing from the region where the leaves are attached.
There is an extensive mythology surrounding the cultivation of Welwitschia, but the plants aren’t as difficult as one might be led to believe. They don’t actually need to be grown in tall, skinny drainpipes, and may in fact benefit from planting in a wide container (or in a ground bed in a greenhouse), which allows room for an extensive network of surface roots to develop. It is possible to transplant them, though Welwitschia roots are a bit on the delicate side. They can also grow fairly quickly: the large mature plants at the University of Connecticut in the photos are only about 12 years old. For the past several summers, these plants have produced cones.
Welwitschia plants are either male or female (i.e., they are dioecious). So far here at UConn, we only have had fully formed cones on male plants like the one in the photo above, but the production of seed should be possible, eventually, as more of our plants reach maturity.
Certain aspects of the reproductive biology of Welwitschia and its relatives in the plant order Gnetales are similar to reproduction in flowering plants, and for a time Welwitschia and the flowering plants were considered to be fairly closely related. More recent information on the evolutionary biology of the vegetable kingdom has pretty well sunk this idea, though, placing Welwitschia and friends much closer to pines and other conifers. Likely fossil relatives of Welwitschia, with similar leaves and reproductive structures, are known from North and South America. Some of the fossil species were apparently tree-like, with branches.