Lotus oroboides (Kunth) Ottley
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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 - Decumbent or ascending, strigose or puberulent (annual-) perennial, with clustered or solitary stems .5-4.5 dm, of superficial or subterranean origin. Leaves diverse and commonly sharply graduated or dimorphic. Lower leaves usually with flattened leafstalk 5-10 mm, subsessile to petioled dependent upon position of lowermost leaflet; leaflets irregularly pinnate (-subpalmate) usually 3 terminal or nearly so, (3-)4-5(-7), obovate (-oblanceolate), 5-12 mm, 1.8-2.5(-3) r. Medial and upper leaves similar to lower leaves, or, more commonly, with reduced leafstalk, often subsessile; leaflets often only 3 and palmate, usually narrower or much narrower and longer, oblanceolate to linear, than lower ones 1-2 cm, 5-20 r. Stipules black glands. Peduncles exceeding subtending leaves; umbels brac-teate or not, with 1-2(-4) ascending or horizontal flowers 1-2 cm. Calyx tube cylindric, 2.5-5 mm; teeth lanceolate or filamentous-subulate, 2-4(-5) mm. Corolla yellow, becoming orange or red, 1-2 cm, usually panduriform; keel oblong or asymmetrically obovate. Ovary straight or curved, with 12-20 ovules; style defined by color, stigma obscurely penicillate. Legume erect or horizontal, oblong or linear, straight or slightly curved, 2-3.5 cm x 2-3 mm, strigose, dehiscent. Seeds few-numerous. Simpeteria.
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Discussion
Lotus oroboides is a subrhizomatous, sprawling or prostrate perennial with reduced stipules, appressed or subappressed pubescence, strongly pedunculate, 1-3 flowered umbels and dehiscent fruits. It is diverse in foliage and flower size. I have defined it on the basis of these listed characters and reasonably consistent corolla morphology, the usually panduriform standard resembling that of L. wrightii and L. utahensis but differing from L. mearnsii, L. greenei and L. rigidus. Between west Texas and southern Arizona, Lotus oroboides usually has petioled, irregularly pinnate leaves. Northward, Arizona to southern Utah, the leaves change from pinnately to subpalmately foliolate and sessile; populations, passing through the L. longebracteatus of current literature, culminate in L. utahensis, which differs also in its erect habit and 2-4 flowered umbels. Lotus wrightii contrasts with L. oroboides in its erect habit, subsessile, palmate leaves, and usually solitary flowers, yet the two are seemingly intergradient. Lotus greenei of southern Arizona and adjacent New Mexico, with villosulous pubescence, and L. mearnsii of northern Arizona with silvery appressed pubescence resemble L. oroboides and the identity of some specimens is ambiguous. Thus Ottley (1944), perhaps reasonably considered many of the northern representatives of L. oroboides to be hybrid populations. The plants in any one region may be either of mostly one or of several types, in the latter instance, possibly including several ecotypes. Ottley (1944) has reviewed the undoubted influence of local environment on phenotypic expression. Genetic infiltration from other species is undoubtedly another source of variance in Lotus oroboides, though perhaps not to the degree alleged by Ottley (1944). Observations suggest hybridization or introgression between L. oroboides and L. rigidus. The leaf form of var nummularius is perhaps a consequence of present or past blending with L. utahensis and possibly also L. wrightii. But there is no experimental evidence for the views of either Ottley or myself. Thus, infraspecific variance in L. oroboides defies facile classification. As treated here, the southern populations of Mexico and the immediately adjacent United States are var oroboides. Overlapping and extending northward to middle Arizona, most plants have broader leaflets and represent var nanus. Further north into Utah, L. oroboides, with usually subpalmate or nearly sessile leaves is var nummularius.
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Distribution
Sw United States and Mexico. Trans-Pecos Texas to s Arizona, n to sw Utah and adjacent Nevada.
United States of America North America| Mexico North America|