Mimosa arturoana M.Morales & Fortunato, 2013

Morales, Matias & Fortunato, Renee H., 2013, A new species of Mimosa (Mimosoideae, Leguminosae) from the inter-Andean dry valleys, Phytotaxa 114 (1), pp. 33-41 : 34-38

Mimosa arturoana M.Morales & Fortunato , sp. nov. Fig. 1 .

Type:— PERU. Amazonas: Luya, Camporredondo, Fundo El Cedro, Ishangas, bosque primario (bosque seco), 1100– 1600 m, 06º07’03’’S, 78º20’02’’W, 29 March 1997, Campos et al. 3716 (holotype BAB!, isotype MO!) .

Differs from Mimosa deamii by armed stems, hispid indumentum, with scaberulous or plumose setae, and craspedia with puberulent valves and scaberulous or plumose hairs in the replum (not unarmed stems, and indumentum of single setae, with uniformly antrorsely strigose craspedia).

Erect shrubs attaining 1.5 m tall. Stems armed with two infrastipular aculei, rare unarmed at some nodes. Indumentum of the vegetative organs with scaberulous or plumose setae, more dense in the apex of stems and inflorescences. Leaves bipinnate, pinnae 1-jugate; stipules 1.5–4 × 0.5 mm, linear-lanceolate or setiform, dorsally pubescent and scarcely setose, weakly 1–3-nerved; petioles 4.5–15.5 × 0.6–1 mm; rachis of pinnae 10–27 mm long; leaflets 11–13 × 3–7 mm, 3–6-jugate, strigose on both surfaces, with unbranched hairs, discontinuously setose margin, 3–4-nerved, oblong to oblanceolate, obtuse, subcoriaceous, secondary nerves not conspicuous. Pseudoracemes shortly exserted or solitary capitula in the axil of contemporary leaves, with the longest peduncles 11–22 mm long, capitula 5–7 × 3.5–5.5 mm in diameter, generally ellipsoid, tenuously hispid before the anthesis; floral bracts 1–1.5 mm long, pectinate-ciliate in the margin, glabrate dorsally, 1- nerved. Flowers sessile, haplostemonous; calyx 0.25–0.5 mm long, campanulate, sometimes with few cilia at apex; corolla 1.75–3.5 mm long, puberulent at lobes; androecium with 4 stamens, filaments (unknown when plentiful flowering) 3.5–5 mm long, free, pink; gynoecium with style 2–3 mm long and ovary 0.5–0.7 mm long, pubescent. Craspedia 16–30 × 4–5 mm, 2–5 articles, oblong to oblanceolate, frequently contracted at base into stipe up to 3 mm long, acuminate or apiculate, plane-compressed, tenuously colliculate over each seed, replum strigose with scaberulous setae; valves densely puberulent. Seeds of ripe fruits unknown.

Taxonomic notes: — Mimosa arturoana is included in subseries Lactifluae , based on the combination of the following characters: A) habit: woody shrubs; B) infrastipular aculei; C) the hispid indumentum; D) the foliar formula (i/3–6); E) fertile haplostemonous flowers ( Fig. 1 ). In its vegetative and reproductive traits, this species is close to several representatives of the subseries Lactifluae occurring in South American Andes and Mesoamerica. The study of five sheets of the type collection (four currently at MO, one at BAB), with flowers and fruits, confirms this should be a new taxonomic entity .

M. arturoana is morphologically close to M. deamii , but the latter has unarmed stems and uniformly antrorsely strigose craspedia, while M. arturoana has armed stems and craspedia with scaberulous or plumose setae in the replum and single, minute hairs in both replum and valves. In addition, the indumentum of M. deamii has single hairs, while the indumentum of M. arturoana has plumose or scaberulous hairs or setae ( Fig. 1G ). These differences in indumentum were frequently the basis of proposals of infrageneric categories in Mimosa , for example, in Mimosa sect. Mimosa ser. Mimosa subser. Brevipedes Barneby (1991: 705) , and between the sections Mimosa and Calothamnos ( Barneby 1991).

Mimosa arturoana also shows affinity with M. lamolina ( Lewis et al. 2010) , but both can be easily distinguished. M. arturoana has variably armed and hispid stems, with scaberulous or plumose setae, especially in the apex, while M. lamolina is unarmed and almost all entirely glabrous. On the other hand, both species differ by the foliar venation: M. lamolina has 3–5 prominent primary nerves and brochidodrome venation, while M. arturoana has 1–3 tenuous primary nerves, and tenuously, eucamptodrome venation ( Fig. 1B–C ). The stipules of M. lamolina are strongly 3-nerved and glabrate dorsally, while the stipules of M. arturoana are nerveless or tenuously 1-nerved and puberulent dorsally ( Fig. 1D ). Although M. lamolina was reported to have whitish green corollas and white stamens, and M. arturoana pink corollas and stamens, these characters have doubtful taxonomic value (at least, in this particular group of mimosas), as was observed by several authors in the field ( Barneby 1991; W. R. Anderson personal observation).

M. deamii , M. arturoana and M. lamolina form a characteristic group of shrubby species of subser. Lactifluae with exserted pseudoracemes or solitary capitula in the axil of contemporary leaves, and few, ample, generally oblanceolate to obovate distal leaflets. In spite of their similarity, the three species can be easily distinguished between them, by their variation in pubescence and venation of leaflets, indumentum of vegetative organs and stipules ( Table 1).

On the basis of the studies performed in the subseries Lactifluae and close taxa, and previous phylogenetic studies ( Simon et al. 2011) we do not consider Lactifluae with rank of series of sect. Mimosa . The distinctiveness of this group seems to be only the habit and geographic distribution, sharing several traits with members of sect. Mimosa ser. Mimosa subser. Polycarpae Barneby (1991: 516) and Pectinatae Barneby (1991: 522) ( Table 1). In addition, the subseries Lactifluae is highly variable in vegetative and reproductive traits. Even more, this group does not appear to be monophyletic, but polyphyletic, related with the other two mentioned subseries ( Barneby 1991; Simon et al. 2011).

In spite of the relationships between the three subseries, M. arturoana differs clearly from the sympatric representatives of Polycarpae and Pectinatae, M. polycarpa Kunth (1819: 8) and M. pectinatipinna Burkart (1947: 523) , by the indumentum, armament of stems, leave formula, form and venation of leaflets, type of calyx and fruits. M. polycarpa has armed stems with infrastipular aculei, and smaller and more numerous leaflets generally glabrous or only setose in the abaxial surface; the indumentum has erect, unbranched setae, and the pods has hispid replum, with long setae. M. pectinatipinna is different by its leave formula, leaflet size, and calyx ( Table 1).

Geographic distribution: — Mimosa arturoana appears to be restricted to the highland areas of northern Peru, specifically in the temperate, dry valleys of Luya province (Amazonas department), in the inter-Andean areas, at 1,100–1,600 m above sea level ( Fig. 2A ) .

The finding of this new mimosa reinforces that subser. Lactifluae has a bicentric distribution, with most of its members in Mexico and Central America, and few species in the dry tropical valleys of the Andes Mountains in South America ( Fig. 2B ).

Contrarily to the expected by their morphologic affinity, the Peruvian species M. incarum and M. lamolina appear more related to other sympatric species of Pectinatae and Polycarpae than M. deamii , in the molecular phylogeny ( Simon et al. 2011). It suggests that the Peruvian Lactifluae evolved by divergence from Mexican ancestors, but the phylogeny of these clades is not still completely resolved. In this context, molecular data from M. arturoana could contribute to clarify the evolution of these allopatric species.

Phenology: — M. arturoana was collected with flowers and immature fruits in March.

Etymology: —The specific epithet resembles Arturo Burkart, who was a distinguished Argentinean botanist and expert of Legumes in his country and around the world.

Figures

FIGURE 1. M. arturoana M.Morales & Fortunato. A) Flowering and fruiting branch. B) Leaflet, adaxial surface. C) Leaflet, abaxial surface. D) Stipule. E) Bract. F) Flower. G) Detail of craspedium (replum and valve’s fragment). Drawn from the holotype.

FIGURE 2. A) Geographic distribution of M. arturoana and M. lamolina in Peru. B) Geographic distribution of M. deamii, M. lamolina and M. arturoana. Circle: M. arturoana. Rectangle: M. lamolina. Triangle: M. deamii.