This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Medicago hispida Gaertn. Fr. & Sem. 2: 349. 1791. Medicago denticulata Willd. Sp. Pl. 3: 1414. 1803.
Annual, branched at the base, the branches spreading or ascending, glabrous or with a few appressed hairs. Leaves petioled; leaflets obovate, rounded, emarginate or obcordate, cuneate, crenulate, 5"-8" long; stipules dentate; flowers few, yellow, 1" long, in small, peduncled heads; pod several seeded, spirally twisted, the 2 or 3 coils flat and rather loose, elegantly reticulated with elevated veins, the thin edge armed with 1 or 2 rows of curved prickles and not furrowed.
In waste places and in ballast about the seaports, Nova Scotia to Pennsylvania, Florida, Nebraska, Texas and also on the Pacific Coast. Bermuda. Fugitive or adventive from Europe. Native also of Asia and widely distributed as a weed. Summer.
M. polymorpha arabica L. Sp. Pl. 780. 1753.
Medicago arabica Huds. Fl Angl. 288. 1762.
Medicago niacttlata Sibth. Fl. Oxon. 232. 1794.
Annual, usually pubescent, with spreading hairs, closely resembling the preceding species, but generally stouter. Leaflets often nearly 1' long, and with a conspicuous dark spot or spots near the centre; pod nearly globose, of 3 or 4 compactly wound coils, reticulate-veined on the sides, the edge thicker and furrowed between the marginal rows of curved prickles.
In waste places and ballast, New Brunswick to Pennsylvania and Georgia. Also on the Pacific Coast. Fugitive or adventive from Europe. Summer. Bur-, heart-, California or spotted-clover. Heart-trefoil. Heart-leaf. Purple grass.