Tuesday, August 14, 2012

Tricky Tick Trefoils, Flowering Fabaceae and Leafy Legumes

Magnificent in magenta, groups of eye-catching Tick Trefoil can be found blooming in sunny locations along the Moira River shoreline during the first week of July. After consulting the species accounts in my field guides and various Internet sources I decided that the plants' attributes were consistent with Showy Tick Trefoil (Desmodium canadense).

Growing all by itself in a much shadier shoreline area in mid-August, the stems and leaves of this Tick Trefoil are more delicate and much less hairy than the plants above, and the flowers have a different aspect. Is this a different species – Illinois Tick Trefoil (Desmodium illinoense) – or are the variances due to habitat?

Tick Trefoils are best distinguished by their loments (the pod-like fruits) so I re-visited the site where the plants in the photos above were growing, and unfortunately there was no sign of any fruits.

Regardless of which species this eventually proves to be it is definitely a beautiful and striking flower that stands out from the crowd.

Tick Trefoil are members of the family Fabaceae (a.k.a. Leguminosae) which includes the clovers (several species in our area), and economically important plants such as peas and beans. Another ubiquitous and showy legume which prefers the same riparian habitat as the trefoil(s) is the Groundnut (Apios americana).

The American Hog Peanut (Amphicarpaea bracteata) has somewhat less flashy flowers but is just as common; this vine flourishes in drier areas along the trail as well as the riverbank.

Originally native to Eurasia and Africa, Crown Vetch (Securigera varia) is planted on this side of the pond along roadside embankments and other areas that require erosion control. Since Fabaceae are symbiotic with nitrogen-fixing bacteria (rhizobia) in their root nodules they also have the added benefit of reconditioning and reclaiming poor soils. Considered an invasive species in some jurisdictions, this plant's pros outweigh its cons ... and besides, masses of Crown Vetch in bloom look nice.

In addition to improving soil fertility many Fabaceae species such as clovers and alfalfas are valued as livestock fodder. On the other hand, some – Bird's-foot Trefoil (Lotus corniculatus), for example – do have their down side. Every grazing animal is potentially the enemy of a plant, and in response many plants have evolved chemical defenses to deter hungry herbivores. Bird's-foot Trefoil's defensive weapon of choice is deadly prussic acid.

Trifolium pratense, better known as Red Clover ... but there are times when "Trifolium" seems to be a misnomer. I have often stumbled across several plants – White Clover and Alsike Clover as well as Red Clover – growing in a relatively small area with leaves sporting four or five leaflets.

And then there's this unusual specimen, where a good number of the leaves had four or five leaflets. Is this due to genetics? Or an abundance of nutrients?

The leaves all appeared discolored ... is this caused by some kind of disease, and does it have some bearing on the plant's multi-leaved growth form?

Curiouser and curiouser – a "green" Red Clover capitulum? No, it appears that the flowers (there were actually two on this plant, a different specimen and location than the multi-leaved one above) are replaced by tiny leaves! If this characteristic is theoretically heritable the plant won't be passing it on to the next generation ... not by means of this particular "flower", in any event.