Monographs Details: Chamaecrista nictitans subsp. nictitans var. mensalis
Authors:Howard S. Irwin, Rupert C. Barneby
Authority: Irwin, Howard S. & Barneby, Rupert C. 1982. The American Cassiinae. A synoptical revision of Leguminosae tribe Cassieae subtrib Cassiinae in the New World. Mem. New York Bot. Gard. 35, part 2: 455-918.
Family:Fabaceae
Synonyms:Cassia leptadenia var. mensalis Greenm., Cassia leptadenia Greenm., Chamaecrista leptadenia (Greenm.) Cockerell
Description:Species Description - Decisively monocarpic but variable in vigor and stature, at anthesis (0.5-)l-6(-8) dm, erect or exceptionally diffuse, when small simple or few- branched from base or middle upward, when stouter bushily branched from near or well above base, the stems distally and lf-stalks simply puberulent with short incurved hairs or both puberulent and thinly setulose with spreading-incurved ones up to 0.4-1.1(—1.3) mm, the lfts usually glabrous on both faces, ciliolate with at least a few, but sometimes random setules 0.4+ mm. Adult lvs (2-)2.5-8(-9) cm; petiole (1.5-)2-5(-6) mm; petiolar gland l(-2), always stipitate, 0.25-0.9 mm diam, in profile tack- or slenderly trumpet-shaped and 0.3-1.3 mm long, almost always taller than diam; lfts of adult lvs (7-)l0-22(-25) pairs, linear or narrowly oblong, up to (3—)4—14 x ±1-3 mm. Pedicels at anthesis 0.5-4, in fruit 2-8 mm; sepals 3-5.6(-6) mm; petals often fading pinkish, 4 equalling or shorter than the longer sepals the fifth, opposed to the short cucullus, commonly but not always exserted, 3.5-7(-7.5) mm, stamens (4-)5-8 the long anthers ±2-3 mm; ovary strigulose or rarely pilosulous; style 0.8-1.5 mm, linear or at tip very slightly dilated, at the stigma 0.2-0.3 mm diam, pod (17-)20-48(-56) x 2.5-3.8(-4) mm, the reddish- or purplish-castaneous, rarely green valves commonly puberulent, sometimes loosely pilose; seeds 2 5-3 2 mm, fuscous or blackish, dull, the lineoles often appearing as lines of fuscous-margined craters.—Collections: 68.

Distribution and Ecology - Arid grasslands, thorn-forest, sandy and gravelly desert slopes and washes, roadsides, and openings in pine-oak- or oak-forest, near sea level on Gulf of California up to 2000 m in n. Sa. Madre Occidental, widespread and following summer rains locally abundant, s.-w. United States from trans-Pecos Texas w. through s.-w. New Mexico to the middle Gila valley and Baboquivari Mts. in s.- centr. and s. Arizona, s. into Mexico along the w. slope of Sa. Madre and around margins of Sonoran Desert in Sonora, through Sinaloa to Nayarit and n.-e. Jalisco; s. Baja California (Sa. de la Giganta and Cape region); and from Texas s. more sparingly along the e. slope of Sa. Madre and margins of the Chihuahuan Desert to Zacatecas and Querétaro, rarely s. to n. Michoacán where passing insensibly into var. jaliscensis.—Fl. VIII-XI, into II s.-ward.

Discussion:

Observers in the United States are accustomed to think of var. mensalis as the western species Cassia leptadenia, admittedly related to eastern C. nictitans but conveniently separated from it in Texas by a gap of some 350 miles which approximately corresponds with the limestone caprock of Edwards Plateau (cf. Turner, 1959, maps 33, 35). However, in the larger view these two entities, which are, or can be, essentially identical in habit, foliage, flower-structure and pod, and differ only slightly in features of pubescence and average pod size, are seen to be northerly outliers of a tropical American complex to which each is inseparably connected by intermediate forms, C. nictitans southward through the West Indies and C. leptadenia southward through western Mexico. The present geographical discontinuity suggests that they arose independently from different immediate southern antecedents and have followed separate paths northward on either side of the Continental Divide; if so, they exhibit a remarkable morphological parallelism, which extends to the often much degraded androecium.

The two differential characters traditionally ascribed to C. leptadenia are a relatively narrow, many-seeded pod, and long-ciliolate leaflets. To these Pennell (1917, p. 341) added a supposed difference in relative length of the odd, long petal, but this has proved a delusion. Turner found (1959, p. 73) that in Texas the stipules of C. nictitans are longer than those of C. leptadenia, but this difference evaporates south of the border. While the pod of typical var. nictitans is indeed, on the average, shorter, wider, and fewer-seeded than that of its western analogue, all recent authors allow some overlap in measurements, and Pullen (1963, p. 55) was reduced to adopting marginal pubescence of the leaflets as the sole reliable criterion. Theoretically feeble though the difference is, especially in the context of sect. Chamaecrista, it is the only absolute one known. Isely (1975, l.c., maps 44, 49) separated the two species by geography alone and so evaded the need for morphological characters.

Internally var. mensalis varies greatly in stature, the stressful climates of the Sonoran Desert and Sierra Madrean arid grasslands having apparently selected thrifty strains which mature very rapidly, like associated desert annuals, and may bear fruits at axils beginning only three or four leaves removed from the cotyledons. But such plants can continue to vegetate and flower so long as moisture and temperature permit. Southward in Mexico coarser and more leafy strains predominate, some of which may perhaps winter-over, although essentially monocarpic. Southward from the valley of Río Grande de Santiago in Jalisco var. mensalis is replaced by var. jaliscensis, different in the dilated style-tip, and in the area of overlap and intergradation commonly more densely setose.

Distribution:Mexico North America| Texas United States of America North America| New Mexico United States of America North America| Arizona United States of America North America| Sonora Mexico North America| Sinaloa Mexico North America| Nayarit Mexico North America| Jalisco Mexico North America| Baja California Mexico North America| Zacatecas Mexico North America| Querétaro Mexico North America| Michoacán Mexico North America| United States of America North America|