|spreading tick-trefoil, tick trefoil, trailing tick-trefoil|
|Elizabeth J. Farnsworth|
The following Participating Institutions are custodians for this species in the CPC National Collection:
New England Wild Flower Society
The conservation of Desmodium humifusum is fully sponsored.
Elizabeth J. Farnsworth contributed to this Plant Profile.
Desmodium humifusum is a prostrate, trailing, perennial herb in the pea family. It is found in dry, sandy, inland forests, ranging from Massachusetts south to Pennsylvania and west to Indiana. Once known from 35 herbarium collections from 19 sites in the northeast, the number of populations has declined, and the species is now ranked as historic in several states: Delaware, Maryland, New Jersey, and New York. Reasons for its demise are largely unknown, but conversion of its habitat, which is conducive to home building, is a likely cause. Its status as a true species or as a hybrid form remains to be resolved, but recent molecular evidence indicates that it is a likely hybrid of Desmodium paniculatum and Desmodium rotundifolium.
This species takes its name, "humifusum" from the words for "earth/ground/soil" (humi) and for "spread out or extended" (fusum), which describe it well. It trails along the ground, with prostrate, hairy stems reaching 1 to 2 m (3.26 to 6.5 ft) in length. "Trefoil" is a French expression referring to its compound groups of three leaves (hairy on both sides) that branch off the stem on slender petioles 2.5 to 5 cm (1 to 2 in) long. Seven to nine small, purple flowers are produced on racemes in July and August.
Distribution & Occurrence
- New Jersey
- New York
Desmodium humifusum inhabits open, dry woods on sandy, acidic soils that have formed from a parent bedrock of sandstone or chert (Gleason and Cronquist 1991, Hanson 2001, NatureServe 2001). As such, the canopy of these woods is likely dominated by oaks (Quercus spp.) and pines (Pinus spp.), and other understory vegetation is probably sparse. It can also occur in power line rights of way (NatureServe 2001).
|Described as "a few scattered remnant populations" (NatureServe 2001). Reported from: Worcester and Suffolk Counties in Massachusetts (Sorrie and Somers 1999); Perry County in Indiana (Indiana Department of Natural Resources 1999); and historically from Bronx, Orange, and Westchester Counties in New York (Young 2001). However, recent analyses of allozymes indicate that the extant D. humifusum populations encompass only 8 genetic individuals, rather than the hundred or so genets previously estimated (Raveill 2002).|
Conservation, Ecology & Research
Pollinators are unrecorded, but may include bees, given the flower color and pollinators recorded for congeners.
As a legume, this taxon may form nodules with nitrogen-fixing bacteria, as do other members of its genus.
According to the Association for Biodiversity Information (NatureServe 2001), plants have been known to withstand herbiciding where they occur in power line cuts.
From allozyme evidence, it is now considered likely that Desmodium humifusum is a hybrid of two parent taxa with which it always co-occurs: D. rotundifolium and D. paniculatum (Raveille 2002). The species also shows morphological characteristics intermediate between these two taxa, lending credence to its hybrid origin.
Habitat manipulation in rights-of-ways
Destruction by off-road vehicles
Shading caused by succession to a dense tree canopy or invasive shrubs
A mention has been made of positively affecting one population of Desmodium humifusum in Indiana through a proposed land acquisition and forest management in the Hoosier National Forest, Perry County, Indiana. (Hanson 2001).
An analysis of the distribution of Desmodium humifusum with respect to environmental variables (e.g., edaphic features, canopy cover, water availability)
Identification of other plant species with which Desmodium humifusum co-occurs
Characterization of plant-animal interactions (pollination, herbivory) and nitrogen-fixing symbionts
Precise counts of plants in each population and measurements of reproductive output
1986. A Checklist of New York State Plants. Contributions of a Flora of New York State, Checklist III. Albany, New York: New York State Museum.
Rhoads, A.F.; Klein, W.M., Jr. 1993. The vascular flora of Pennsylvania: Annotated checklist and atlas. Philadelphia, PA: American Philosophical Society. 636p.
Shetler, S.G.; Orli, S.S. 2000. Annotated checklist of the vascular plants of the Washington-Baltimore area. Part I. Ferns, fern allies, gymnosperms, and dicotyledons. Washington, D.C.: National Museum of Natural History.
Sorrie, B.A.; Somers, P. 1999. The vascular plants of Massachusetts: a county checklist. Westborough, Massachusetts: Massachusetts Natural Heritage and Endangered Species Program.
Wherry, T.E.; Fogg, J.M.; Wahl, H.A. 1979. Atlas of the flora of Pennsylvania. Philadelphia, Pennsylvania: Morris Arboretum.