Purple bushbean (Macroptilium atropurpeum) sure is pretty with its dark, dark purple flowers. Thank you to George Bollis for the beautiful pictures of this plant taken near Lake Keanan and to Mary Ester Bollis for sending me his photos correctly identified.
At a glance, you might mistake it for wild bushbean (Macroptilium lathyroides), a not uncommon weed at the Oslo Riverfront Conservation Area (ORCA) shown below.
The flowers of wild bushbean are a much lighter red-purple color. Wild bushbean is an herbaceous annual or a very short-lived perennial, while purple bushbean is a perennial plant with a deep, swollen taproot. Native to Mexico, south American and the Caribbean, both bushbeans are used as tropical forages and have trifoliate leaves. The leaves of purple bush bean have fine hairs on the upper surface, the undersides of the leaves are grey-green and pubescent, and the leaflets are more lobed.
The seeds of purple bushbean, shown above in another magnificent photo from George Bollis, are forcibly ejected its pods up to several feet. Seeds also are spread via water and by cattle that ingest them.
As fodder, this plant is not a weed. In a garden or natural area, it may not be so welcome.