Macrosamanea arenicola (R.S. Cowan) W.L. Silva, Iganci, M.P. Morim & J.U. Santos, 2016

Silva, Wanderson Luis Da, Morim, Marli Pires, Iganci, João Ricardo Vieira & Santos, João Ubiratan Moreira Dos, 2016, New combination in Macrosamanea (Leguminosae-Mimosoideae), Phytotaxa 288 (2), pp. 187-192 : 188-190

Macrosamanea arenicola (R.S. Cowan) W.L. Silva, Iganci, M.P. Morim & J.U. Santos , comb. nov. ( Fig. 1a–c )

Basionym:— Pithecellobium arenicola R.S. Cowan, Memoirs of The New York Botanical Garden 10(4): 67–68, fig. 46. 1961.

Type:— VENEZUELA. Amazonas: occasional in savanna on right bank of Rio Pacimoni 50 km above mouth, alt 100–140 m, 07 February 1954 (fl.; fr.), Bassett Maguire, John J. Wurdack & George S. Bunting 37568 (holotype US[00000309, 00000332]!, isotypes US [00651759]! NY [00334619]!) .

Macrosamanea discolor var. arenicola (R.S. Cowan) Barneby & J.W. Grimes, Memoirs of The New York Botanical Garden 74(1): 193. 1996. syn. nov. .

Small trees up to 4 meters, erect or rare sparsely branched, branches lenticellate, glabrous or pubescent. Stipules lanceolate, 1.5–5.5 mm long, deciduous. Leaves with 1–2 pairs of pinnae; petioles 0.9–16 mm long, glabrous or pubescent; rachis 1.4–3.6 cm long, glabrous or pubescent, nectaries 1–2, between each pair of pinnae, 2.5–4 mm diam, sessile, elevate-concave, elliptic, sometimes expanded (with 1 pair of pinnae), ovate to suborbicular (when second pair present). Leaflets 14–26 pairs per pinna, 1.8–3.2 × 0.5–0.8 cm, oblong-lanceolate (proximal pairs), lanceolate (distal pair), base usually asymmetric, rounded, apex acute or mucronulate, glabrous or pubescent on the abaxial surface, midrib eccentric, forwardly displaced to divide blade 1:2, secondary veins inconspicuous on adaxial surface, brochidodrome, nectaries located between all of leaflet pair, 1–3 mm diam sessile. Inflorescences in compound raceme with condensed lateral axes in pseudoraceme of capitula, 3–7 flowered, terminal or subterminal, peduncles 0.4–1.6 cm long, receptacle clavate, 1–2 × 2–4 mm; bracts 2.5–4 mm long, deltate, nectaries pateliform, conspicuous; perianth 5– parted. Flowers homomorphic, sessile; calyx 6.5–13 × 3–4 mm, cylindro-campanulate, green, strigose, lobes 2.5–3.5 mm long; corolla 15–24 × 3–4 mm, infundibuliform, white or green, strigose, veins indistinct, lobes 5.4–6 mm long; stamens 80–120 per flower, staminal tube longer than corolla, stemonozone 4–6 mm long, filaments white or rosewhite; 1 carpel, style linear, up to 1 cm longer than filaments, stigma not dilated. Fruit a follicle, 5.1–7 × 2.2–3.5 cm, subsessile, oblong, flat-compressed, erect or slightly curved, base obtuse, apex obtuse with a short mucron, strigose, brown when mature; seeds unknown.

Taxonomic notes: — Pithecellobium arenicola was described by Cowan (1961: 67) based on specimens collected in Venezuela by B. Maguire in 1954. The species was distinguished from Pithecellobium aquaticum (Pittier) R.S. Cowan (1961: 67) (a synonym of Macrosamanea discolor ) based on the leaflet shape, the presence of quite conspicuous glands on leaves and inflorescences, and the habitat.

Pithecellobium arenicola was combined with Macrosamanea discolor var. arenicola by Barneby & Grimes (1996), who considered this taxon as having a similar morphology and geographical distribution to Macrosamanea discolor , justifying their proposed infraspecific taxonomic status. These taxa were distinguished by differences in the veins of the leaflets, peduncle length, calyx/corolla length, and habitat ( Barneby & Grimes 1996). Variations in the inflorescence and indumentum type of the calyx/corolla were not mentioned.

Inspection of a new collection (Redden 3681, NY) revealed that some of the characters defined by Barneby & Grimes (1996) to distinguish the two taxa do indeed overlap in their measurements (corolla and calyx size).

However, we observed enough new and additional morphological characters to justify considering Macrosamanea arenicola as a distinct species from M. discolor , in that the former has a compound raceme (vs simple raceme), indumentum of calyx and corolla strigose (vs puberulent) and corolla veins indistinct (vs evident) ( Table 1; Fig. 1 ).

Distribution, habitat and phenology: — Macrosamanea arenicola is known only from the enclaves of white sandy savanna and savanna-forest ecotone, Amazonian caatingas and campinas along both banks of the Orinoco- Negro River and its tributaries: Atacavi, Casiquiare, Cucurital, Pacimoni, Siapa (Venezuela-Amazonas: Atabapo and Rio Negro) and Uaupés (Brazil-Amazonas: São Gabriel da Cachoeira), at about 80–140 m elev. ( Fig. 2 ). Herbarium records indicate that M. arenicola flowers from November to May, and fruits from November to February.

Conservation: — Macrosamanea arenicola occurs sparsely within its geographical range, and has a fragmented distribution. This taxon is known from only 11 localities, and none of the specimens were found inside protected areas. These localities were imported into GeoCAT ( Bachman et al. 2011; cell size 2 × 2 km), and the area of occupancy (AOO) was estimated to be 44 km ² (Endangered), while the extent of occurrence (EOO) was estimated to be 42,416 km ² (Near Threatened). However, the high habitat specificity and the distribution of this species along rivers makes it relatively vulnerable to human impact, mainly from sand mining and artisanal gold mining ( Lasso et al. 2006). Thus, declines in the AOO, extent and quality of habitat, number of individuals and number of subpopulations can be predicted. Based on the present observations and following the IUCN criteria ( IUCN 2014), we conclude that M. arenicola should be assigned the preliminary status of “Endangered” [A1c; C2a(i)].

Widely distributed and abundant species are generally considered to be less threatened than narrowly distributed, rarer species. The newly raised taxon M. arenicola must be considered as a unit for conservation purposes, and we are beginning to evaluate its distribution range and abundance in order to establish the IUCN conservation status. Recognition of a new taxonomic status improves estimations of the numbers of species within a flora.

Vernacular name: —“Arepillo” or “Guamita” ( Venezuela). No vernacular name is known for this species in Brazil.

Etymology: —The specific epithet, from the Latin arenicola (dweller in sand), refers to the sandy savanna soils to which the species seems to be restricted.

Additional examined material:— BRAZIL, Amazonas: São Gabriel da Cachoeira, Alto Rio Negro , Rio Uaupés , Igarapé Tibuarí , acima do Seringal Pago , 22 November 1987, H. C. de Lima 3276 ( INPA, RB, NY). Amazonas : São Gabriel da Cachoeira , Alto Rio Negro , próximo à boca do igarapé Tuari , Lago Amaro , do lado oposto à Ilha de Aparecida , 0°20’N, 67°19’W, 6 November 1987, W. A. Rodrigues 10868 ( MG, RB, INPA, NY) ; VENEZUELA, Amazonas: Casiquiare, frequent in savanna on left bank of Caño Hechimoni , 8 km above mouth, alt. 100–130 m, 9 February 1954, Bassett Maguire, John J. Wurdack & George S. Bunting 37624 (paratype NY [01420363]!) ; Amazonas: Atabapo, Cucurital de Caname , southern bank of the middle part of Caño Caname, 3°40’N, 67°22’W, 30 April 1979, G. Davidse 16923 ( NY) ; Amazonas: Atabapo, Northern bank of Caño Caname , nearly opposite Cucurital de Caname , 3°40’N, 67°22’W, 2 May 1979, G. Davidse 17033 ( NY) ; Amazonas: Atabapo, Laja Cucuta, en El Rio Atacavi , Pica 1, Frente no 3, 3°12’N, 67°24’W, November 1989, J. Velazco 1064 ( NY) ; Amazonas: 24-savannah behind base camp 9, 1°56’5”N, 66°41’48.6”W, 11 Februaty 2005, K. M. Redden 3681 ( NY) ; Amazonas: Atabapo, Caño Caname (afluente derecho del medio Río Atabapo ), sabanas de Cucurital, 3°40’N, 67°22’W, 29 April 1979, O. Huber 3655 ( NY) ; Amazonas: Rio Negro, pequeña sabana ubicada en la márgen derecha ( E) del bajo Río Pasimoni , a unos 3 km del Río, 1°38’N, 66°32’W, 9 February 1981, O. Huber 5879 ( INPA, NY) ; Amazonas: Rio Negro, Río Chimoni, tributary of the Siapa River , 8 turns upstream from mouth, February 1989, Stergios 13284 ( NY) ; Amazonas: Río Negro, Río Pasimoni , en la “Sabana Grande”, a altura de Pueblo Viejo, February 1989, Stergios 13326 ( NY) ; Amazonas: Río Negro, selvas ribereñas y caatinga de arena blanca del Rio Pasimoni. Expedicion venezolana del Proyecto de Botanica Amazonica del Tratado de Cooperacion Amazonica a la cuenca del Brazo Casiquiare, 3 February 1992, Stergios 15553 ( NY) .

Figures

FIGURE 1. A–C. Macrosamanea arenicola (R.S. Cowan) W.L. Silva, Iganci, M.P. Morim & J.U. Santos. (Rodrigues 10868, MG), A. Inflorescence. B. Flower with detail of the calyx indumentum. C. Leaflet. D–F. Macrosamanea discolor (Humb. & Bonpl. ex Willd.) Britton & Rose ex Britton & Killip (D: Goulding 55, MG; E–F: Lima 7367, RB), D. Inflorescence. E. Flower with detail of the calyx indumentum. F. Leaflet.

FIGURE 2. Geographic distribution of Macrosamanea arenicola (R.S. Cowan) W.L. Silva, Iganci, M.P. Morim & J.U. Santos (●) and Macrosamanea discolor (Humb. & Bonpl. ex Willd.) Britton & Rose ex Britton & Killip (▲).