Lotus purshianus Clem. & E.G.Clem.
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Authority
Isely, Duane. 1981. Leguminosae of the United States. III. Subfamily Papilionoideae: tribes Sophoreae, Podalyrieae, Loteae. Mem. New York Bot. Gard. 25 (3): 1-264.
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Family
Fabaceae
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Scientific Name
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Description
Species Description - Erect or prostrate, strict or branched at or above base, glabrate to moderately pilose annual .5-6 dm; branches commonly 2-ranked. Leaves subsessile or shortly petiolate, pinnately trifoliolate, or the upper, or most blades simple; leaflets ovate, elliptic, or lanceolate, acute, the medial (.5-) 1-1.5(-2.5) cm, 2-5 r. Stipules inconspicuous glands. Flowers axillary, solitary, (4-)5-9 mm, pedunculate .3-1.5 cm, shortly pediceled above a simple bract. Calyx tube 1-2 mm, teeth 2-4.5 mm. Corolla initially ochroleucous, aging pinkish or salmon-pink; standard becoming reddish-striate; keel yellow-tipped; wings ± keel. Ovary with 6-7 ovules; style defined, abruptly angled upwards 45°; stigma not penicillate. Legume divergent or declined, straight or slightly curved, (1.5—)2—3 cm, dehiscent; valves glabrate or hirsute. Microlotus.
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Discussion
Lotus purshianus is the only native Lotus of the central and eastern states. It bears no resemblance to the introduced L. corniculatus, which is common in the north. In the Pacific states, where L. purshianus has numerous relatives, it is recognized by its pedunculate solitary flowers, 1-3 foliolate leaves and long calyx lobes. Lotus purshianus, presumably deriving from the west is the most successful North American species in terms of natural range extension. It occupies three disjunct areas: the Pacific and adjacent states where omnipresent; the central Plains states where widely distributed but common only in the south; and a sharply congruent unit in the eastern Piedmont. It is essentially absent in the intervening mountain and intermountain provinces and in the eastern states except for the southeastern var helleri. Possibly its distribution was at one time transcontinental and in much of the central states occurrence is now semirelictual. Variability in Lotus purshianus is greatest in California. Plants may be either erect, or prostrate and mat-forming, glabrate or pubescent. If erect, they may be strict and unbranched, stiffly ascending-branched, or diffusely bushy and as wide as high. The petioles are elongate or reduced, and the peduncles and pedicels short to slenderly arcuate. The leaves, usually trifoliolate, are sometimes mostly simple. Upper elevation plants are usually diminutive with small flowers. Numerous combinations of these characters are possible, and many are achieved in various ecotypes and races. Nuttall named several species among members of this complex, and these were taken up and supplemented by Heller (loc. cit.). It is true that there is some ecological and geographic ordering of some of these forms: e.g., var. minutiflorus Ottley is a reduced, upper elevation ecotype and L. aestivalis Hell, is later flowering than others. Authors presently agree in considering them manifestations of one species. Lotus helleri, which I have reduced to varietal status, however, has previously been treated as an independent entity.
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Distribution
United States and adjacent Canada and Mexico. Pacific states and w Idaho; central plains and prairies, Dakotas and Minnesota to Texas and Arkansas; the Carolinas and adjacent states. Habitats diverse. May-Sept. (-Nov.).
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