Lotus wrightii (A.Gray) Greene

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.

Family

Fabaceae

Scientific Name

Lotus wrightii (A.Gray) Greene

Description

Species Description - Stiffly erect or sprawling, basally branched, strigose (-subcanescent) perennial 2-4(-8) dm with clustered and branched stems commonly reddish below. Leaves 3-6 foliolate, often moderately dimorphic, the lower palmate or subpinnate with broader leaflets, the medial and upper subsessile or sessile, palmately foliolate and sometimes subtending secondary clusters of filiform leaflets; primary leaflets obovate, oblanceolate or linear, acute, the medial 8-20 mm, (3-)4-10(-15) r. Stipules black pointed glands. Umbels usually sessile (-peduncled 3-4 mm), with l(-2) ascending or deflexed flowers 1-1.5(-1.8) cm. Pedicels 1-2 mm. Calyx tube 3.8-5 mm, teeth 3-4.5 mm, subulate to setaceous. Corolla yellow, becoming reddish, regularly graduated; standard slightly panduriform. Stamens of alternating lengths. Ovary glabrate or strigulose; ovules 15-18; style abruptly defined; stigma obscurely penicillate. Legume divergent or declined, 2-3.5 cm x 1.5-3 (-3.5) mm, dehiscent, valves strigose or glabrate. Seeds few-many. Simpeteria.

Discussion

Hosackia wrightii Gray (1853); L. wrightii (Gray) Greene (1890); Anisolotus wrightii (Gray) Rydb. (1906). L. oroboides auct. pro parte. Lotus wrightii is typical of yellow pine woodlands of north-central Arizona where it is common and unmistakable, the diagnostic features being its ascending habit and usually subsessile, axillary flowers. But if seen through its entire range, L. wrightii becomes harder to define because of variance in habit, vigor, calyx teeth length and shape, level of pubescence, flower size, and peduncle development. While most of this phenotype plasticity is probably taxonomically unimportant, some is probably due to hybridization or introgression with related species. Espousing this belief, Ottley (1944) reported presumed hybrids of Lotus wrightii with L. rigidus, L. utahensis and L. mearnsii, but I can scarcely validate her assumptions. Plants with pedunculate peduncled umbels from Arizona that she believed represented L. rigidus x wrightii have none of the features of the former species save the peduncles. Some deviant specimens might, in part, owe their features to L. mearnsii. Those that look like L. wrightii x utahensis do not lie within the range of the latter species. I have grouped the more repetitive “deviant” forms as follows: Phase 1. Flowers pedunculate .5-2 cm; plants probably commonly spreading, primarily of the southern part of the range. Phase 1 usually seems not to blend with the typical form. I don’t know whether these plants are within- or between-population variants, or whether they constitute a coherent variety. If they are manifestations of introgression from another species, Lotus oroboides is the most likely candidate, some specimens, except for assumptions of habit (often not clearly discernible on mounted material) being scarcely distinguishable from L. oroboides. But floral dissections reveal no differences from typical L. wrightii. Phase 2. Flowers 1-2(-3), the umbels pedunculate 1-3 cm, southern. Some of this phase are similar to Lotus utahensis but are not contiguous to the range of that species. The majority have narrow leaflets, narrowly subulate calyx lobes, and their habit is uncertain. They are especially common in the southern Arizona desert mountains. Possibly they also are L. wrightii x oroboides derivatives, but some with long internodes might have L. wrightii x rigidus ancestry.

Distribution

C to ne Arizona, nw New Mexico and adjacent corners of Utah and Colorado. Mostly of yellow pine forest; also with aspen; downwards to juniper and oak, in the open or under trees; canyon slopes, mesas, washes; various soil types. Ca. 4000-9000 ft. (May-) June-Sept.

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