Mimosa borealis
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Title
Mimosa borealis
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Authors
Rupert C. Barneby
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Scientific Name
Mimosa borealis A.Gray
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Description
57. Mimosa borealis A. Gray, Mem. Amer. Acad. Arts II, 4(Pl. fendler., novi-mex.): 39. 1849.— "[.A. Fendler] 181 ... Hillside, Upper Spring, on the Cimarron; August."—Holotypus (Isely, 1971b: 416): GH!
M. fragrans A. Gray, Boston J. Nat. Hist. 6:182.1850. — "... on the Pierdenales [Pedemales], April, in flower ([Lindheimeri] 606); May, with fruit (607)."—Lectotypus (Isely, 1971b: 416): Lindheimer 607, GH!; iso- and syntypi, NY!
Stiffly branched microphyllous shrubs attaining 12 dm but often depressed and as wide as tall, the usually straight, pungent-tipped long-shoots randomly armed on intemodes with solitary broad-based, brown-tipped or in age blanched, straight or gently recurved, remotely infrapetiolar aculei 2—9 mm, glabrous except for minute tufts of crimped hairs on margin and inner face of brachyblast-stipules, at tip of most lf-stks and pinna-rachises, and on margin of calyx and corolla-lobes, the firm pale-green lfts concolorous, the umbelliform, spherical or hemispherical capitula solitary and geminate, fasciculate with lvs on hemispherical brachyblasts along annotinous branches, often forming long lf-bracteate pseudoracemes. Stipules of primary lvs 1.5-3.5 mm, externally nerveless or 1-nerved, those of brachyblasts triangular-subulate. Leaf-formula (o-)i-iii(-iv)/(2-)3-7(-8), the pinnae of most primary lvs at least 2-jug., of most brachyblast-lvs 1-jug., exceptionally a few lvs simply pinnate; lf-stks (l-)3-30 mm, the petiole (1—)3—12 mm, bisulcate ventrally, the rachis (when present) 1-sulcate, spicules 0; rachis of conjugate pinnae (1.5—)3—12 mm, of distal pinnae of some primary lvs rarely attaining 25 mm, the lfts narrowly oblong or elliptic-oblanceolate to -obovate, weakly (l-)2(-3)-nerved dorsally, the longest ±3-6(-6.5) x 1-2.3 mm. Peduncles at anthesis subcapillary (7-) 10-23 mm; capitula without filaments 5-7 mm, prior to anthesis moriform; pedicels 0.4-1 mm; flowers (4-)5- merous diplostemonous; calyx turbinate 0.5-0.8 mm, the rim minutely denticulate; corolla turbinate 2.1-2.8 mm, the lobes free or almost so, the obtuse blade of each narrowed to a claw, this united with filaments into a stemonozone 0.30.4 mm; filaments pink, exserted (2.5-)3-4.5 (-5) mm; ovary stipitate glabrous. Pods 1-5 per capitulum, glabrous overall, in profile undulately linearly, arched downward, the seminiferous body 25-60 x 6-10 mm, 3-8-seeded, contracted at base into a stipe 4-9 mm, cuspidate at apex, the stout, usually deeply constricted replum smooth or randomly aculeate (especially along adaxial suture), the stiffly papery valves green subglau- cescent, brown when ripe, bullately distended over each seed, tardily breaking up into articles 6— 10(— 12) mm long.
In thorn-scrub, on gullied hillsides and eroded bluffs, becoming weedy on road-cuts and overgrazed rangeland, ±400-1250 m, preferring calcareous substrates, locally abundant, from upper Cimarron valley in far s.-w. Kansas and s.-e. Colorado s. through the Pecos valley in e. New Mexico and over the high plains to the s. edge of the Edwards Plateau in Texas (Isely, 1973, map 33, excluding some records for trans-Pecos Texas, referable to M. tumeri; cf. protologue, fig. 1).—Fl. IV-VI(-VII).
Notably different from kindred species in co- rolla-lobes free almost to base (Barneby, 1986, fig. 2).