CRANDALL-STOTLER, BARBARA. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509. - Biology and evolution of the Fossombroniineae.
Investigations into the biology of the four genera of the
Fossombroniineae has resulted in several unexpected discoveries, a few
of which will be detailed in this presentation. For example, although
generally regarded as soil-dwelling, r-selective annuals of disturbed
habitats, many species of Fossombronia are actually
perennial-stayers and some may even form extensive mats over rocks and
roots. Populations are often comprised of single genets which are
self-fertile, spore dispersal is local and gene flow between
populations is low. Cosmopolitan taxa are anthropogenic and endemics
are common. Austrofossombronia comprises several turf-forming
species, distributed not only on Antarctic Islands, but also at high
elevations around the world. Within the suborder three different
mechanisms of drought tolerance and/or avoidance have evolved. These
include 1) forming dormant, fleshy stems, with whitened leaves which
may regreen on wetting, 2) developing subterranean tubers, and 3)
forming endospore-like, endogenous gemmae. Anatomical studies verify
that Petalophyllum and Sewardiella form pseudoperianths
and shoot calyptrae, but that Fossombronia and
Austrofossombronia form a developmentally distinct, analogous
structure, here termed a caulocalyx. Preliminary molecular data
suggest that Petalophyllum is basal in the suborder and that
Fossombronia is derived.
Key words: Austrofossombronia, drought response, Fossombronia, molecular phylogeny, population dynamics, shoot/sporophyte associations