Stylosanthes hamata and additional species
The first time I saw Cheesytoes (what a name!) was on a rough roadside a few years ago—the kind of scratchy place you change a flat tire. The Cheesytoes seemed to fit in among the coarse exotic weeds there. Not recognizing the posie, I keyed it out and was pleased to greet a native species. Who knows, maybe it was rising defiantly from the original scrubby soil seedbank underlying the thoroughfare. At least cultivar ‘Verano’ (see below) withstands herbicide attack, which may help explain the roadside living of today’s plants.
Rising from an old seedbank is plausible, because species of Stylosanthes have particularly hard durable seeds. This matters in a crop plant when you wish to reap and sow, and a recent (2011) study in Grass and Forage Science suggests microwaves to get the party started with one Stylosanthes species.
Styloanthes is an odd little genus. There are more or less 25 species, 23 of them in warm America and two in the tropical Old World. Florida has three species, more or less: Stylosanthes biflora is widespread rom Central to North Florida. Some native plant nurseries sell it. Why not? Tough, undemanding, and attractive in a rascally way. Stylosanthes calcicola occupies the very southern tip of Florida and is state-listed as endangered. Native to our botanical home range is S. hamata.
Species of Stylosanthes interface with human activity mainly in the pasture. They are legumes for varied and trying circumstances. They fix nitrogen and have an unusual ability to extract phosphorus from the substrate. Not bad, let’s see, fix nitrogen, extract phosphorus, and oh yes, as an added rancher bonus the plants repel ticks. All of these things have prompted fodder plantings from China and Australia to Brazil.
Our own Stylosanthes hamata is historically a broadly defined species, or “species plus some.” Taxonomic studies, chromosomal observations, biochemical data, and DNA work have combined over the years to show the “species” to be a mix of diploid plants (having one set of chromosomes) and hybrid strains with extra chromosome sets derived from other species, in other words a genetic hodgepodge. The “Stylosanthes hamata” cultivar ‘Verano’ is a combination of two species. So then, cryptic genetic pollution of a native population by alien cultivated material is possible, similar to the situation in Phragmites reeds.
In Florida both diploid (two chromosome sets) and tetraploid (four chromosome sets, probable hybrids) occur. Wouldn’t it be fun to look into that in detail? Diploid and tetraploid “S. hamata” strains behave differently: the diploids require alkaline soil but the tetraploids do not; the diploids seem to be less drought tolerant; the diploids seem to require long days for flowering; and at least some tetraploids seem to be herbicide-resistant. This, however, is all based on narrow data with the knowledge that there are multiple tetraploid strains. So overgeneralization is very possible, but maybe those extra chromosomes confer added protections against adversities.
Not long ago in this blog we looked at fruits on Sea Rocket, finding that they snap into two segments, one remaining on the parent plant on a proven favorable habitat, and the other hitting the road dispersal-wise. Here it is again. In Sea Rocket the wandering brother floats away. In Cheesytoes, the wanderer has a hook to snag a passerby and saying farewell to the homebound segment. Oh, btw, “hamata” means hooked.