Mimosa chochisensis Atahuachi & C.E. Hughes, 2016

Atahuachi, Margoth, Bent, M. Leontien Van Der, Wood, John R. I., Lewis, Gwilym P. & Hughes, Colin E., 2016, Bolivian Mimosa (Leguminosae, Mimosoideae): three new species and a species checklist, Phytotaxa 260 (3), pp. 201-222 : 206-208

Mimosa chochisensis Atahuachi & C.E. Hughes , sp. nov. ( Fig. 3)

Closely allied to M. jacobita Barneby (1991: 648) and M. bipennatula Barneby (1991: 647) , but differing from both these species in much longer pinnae (8–10 cm compared to <4 cm), markedly larger leaflets (> 10 mm wide compared to <4.5 mm), presence of paraphyllidia, larger flowers and capitula, and more robust habit.

Type:— BOLIVIA. Santa Cruz: Provincia Chiquitos, N side of the Serannía de Chochis , entering by El Portón, 627 m, 18°06´53´´ S, 60°03´26´´ W, 5 May 2008, (fl), J. R. I. Wood et al. 24702 (holotype LPB!; isotypes K!, UB, USZ!) .

Slender erect unarmed shrublet to 1.5 m, the spindly defoliate trunk branched distally, the sub-vertical microphyllidious leaves crowded towards tips of branches, the hornotinous shoots and leaf stalks densely strigose with forward pointing closely appressed, smooth, stramineous, basally dilated, (2–) 3–4 mm long setae, the small plumply ovoid capitula solitary or in fascicles of 2–3 in leaf axils of developing leaves, the fruits immersed in foliage. Stipules erect, firm, narrowly lanceolate, (10–) 12–14 × 1 mm, with 3 (–5) prominent longitudinal ribs on abaxial surface, densely setulose on margins with short 1–2 mm long basally dilated setulae, but otherwise glabrous, green turning livid castaneous, persistent. Leaves bipinnate, consistently 1-jugate, the pinnae erect from a narrowly ascending 10–15 (–18) mm long petiole, rachis of longer pinnae 7–12 cm with (39–) 60–70 pairs of leaflets, these densely overlapping along pinnae, narrowly linear acute, those near mid-rachis 10–12 × 1.5–1.8 mm, the blades veinless and glabrous above, beneath finely sub-centrically 1-veined, continuously marginate and densely setulose with appressed pale cream setae below, the lower pair of leaflets reduced to setiform paraphyllidia, these often obscured amongst setae. Peduncles sturdy, 8–12 mm, densely setulose; capitula without filaments to 5–7 mm diam., prior to anthesis cone-like, the bracts exserted in bud, these oblong spathulate 2–3 × 0.6 mm and densely setulose; flowers 4-merous, 4-androus, the lower ones frequently staminate; calyx paleaceous to 2 mm, almost as long as corolla, the lobes united into a tube ± 0.5 mm, lacerately and unevenly divided above; corolla turbinate, 1.8–2.2 × 0.5 mm, the membranous tube glabrous, the lobes antrorsely setulose; filaments pink, obscurely united at base below ovary. Fruits sessile or nearly so, in clusters of 6–12 per capitulum, linear-oblong, round at base, with a terminal cusp, (20–) 23–25 × 6–8 mm, 3–4-seeded, the replum densely strigose with basally dilated stramineous setae to 3 mm, the valves also short setulose over seed chambers, breaking up readily into indehiscent one-seeded articles to leave a persistent replum, the replum often splitting at apex to leave persistent simple pod margins after pods break up.

Distribution and ecology: — Mimosa chochisensis is a narrowly restricted endemic from the escarpments and rocky hills of the Serranía de Chochis in the immediate vicinity of Chochis. It is scattered but locally frequent on crumbling rocky slopes and rocky platforms in open dry forest and campos rupestres vegetation around the base and atop the rocky pillars and formations of El Torre and Cerro Pelón.

Additional specimens examined: — BOLIVIA. Santa Cruz: Prov. Chiquitos, Chochis, by path going around base of La Torre, 650 m, 27 December 2002 (fl, fr), J.R.I. Wood 18792 (K!, USZ). Santa Cruz: Prov. Chiquitos, Cerro Pelón, above Mina Soledad, NE of Chochis, 700 m, 20 July 2000 (fl), J.R.I. Wood 16482 (K!, USZ!). Santa Cruz: Prov. Chiquitos, Chochis, at base of La Torre, above El Sanctuario, 18°04´30´´ S, 59°01´30´´ W, 17 March 2005, J.R.I. Wood 21888 (K!, USZ!). Santa Cruz: Chiquitos, Chochis, near the pass across the Serranía de Chochis on the path from Chochis to Motacuzal, 18°03´S, 59°34´48´´ W, 17 March 2005, J.R.I. Wood & A. Haig 21900 (K!, USZ!). Santa Cruz, Chiquitos, km 15 old road Taperas to Roboré, 498 m, 18°02´35´´ S, 60°24´29´´, 26 November 2009, W, J.R.I. Wood et al. 26504 (K!, USZ!). Santa Cruz, Chiquitos, main road Taperas to Roboré near Ipias, 415 m, 18°00´17´´ S, 60°13´19´´ W, 26 November 2009, J.R.I. Wood et al. 26515 (K!, USZ!).

Phenology: —Flowering (December) January to May; fruiting March to July.

Etymology and Conservation Status: — Mimosa chochisensis is known only from the immediate vicinity of Chochis, and although locally frequent, is globally rare as far as our present knowledge goes.

Notes: — Mimosa chochisensis shows clear morphological similarities to species of Barneby’s (1991) subseries

Bipennatulae of ser. Mimosa , sect. Mimosa , including characteristic rupestral slender fruticulose habit with the leaves generally clustered towards tips of stems, a distinctive paleaceous calyx to> 2 mm, and 1-jugate leaves with numerous pairs of contiguously packed narrow and continuously marginate leaflets. These affinities are confirmed by the robustly supported (PP=1.0) placement of sequences of two accessions of M. chochisensis in Clade S of Simon et al. (2011) ( Fig. 1), a clade that includes M. jacobita of subser. Bipennatulae along with some species of subser. Pudicae , including M. xanthocentra .

The three species of subseries Bipennatulae , M. jacobita , M. bipennatula and M. chochisensis , form a morphologically and ecologically coherent series of closely allied species with distinctive campo rupestral ecology, all three of them occupying narrowly restricted allopatric ranges scattered across the residual dry rocky serranías on either side of the upper Río Paraguay in eastern Bolivia and adjacent Brazil — M. bipennatula in the east, known only from the Chapada dos Guimãraes, Mato Grosso, Brazil, M. jacobita extending along much of the Serranía de Chiquitos, and M. chochisensis to the west, endemic to the rocky hills in the immediate vicinity of Chochis—a geographic pattern of allopatric distributions on mesetas on either side of the Rio Paraguay seen amongst other pairs and small clades of putative sister species within Mimosa (e.g. for M. dalyi Barneby (1984: 249) and M. insignis ( Hassler 1919: 152) Barneby (1984: 249) ; M. josephina Barneby (1991: 483–484) and M. rojasii Hassler (1910: 9) ; M. orbignyana , M. aguapeia Barneby (1991: 363–364) and M. riedelii Bentham (1846: 91–92)) ( Barneby 1991) .

Mimosa chochisensis can be readily distinguished from the other two members of subseries Bipennatulae , M. bipennatula and M. jacobita , based on quantitative leaf and pod traits, and most notably the much longer pinnae, dramatically larger leaflets, and larger flowers ( Table 2) ( Fig. 3; Barneby 1991: 647, Fig. 22), in addition to the more robust habit.

Barneby (1991) pointed out the similarities of subseries Bipennatulae to some members of subseries Pudicae and most notably M. xanthocentra , a relationship confirmed by the molecular analysis of Simon et al. (2011) ( Fig. 1). Mimosa chochisensis can for the most part be readily distinguished from M. xanthocentra in lacking armature and rupestral fruticulose habit as in large part M. xanthocentra is armed and functionally herbaceous. However, subspecies subsericea of M. xanthocentra can be unarmed and sometimes shrubby and is then very similar to M. chochisensis , and only distinguishable by the continuously marginate leaflets, specialized spindly rupestral habit and insensitive pulvini at the base of the leaf stalk and pinnae, all of these characteristic of subseries Bipennatulae .