Mariosousa durangensis (Britton & Rose) Seigler & Ebinger
Synonymy and types
Acacia durangensis (Britton & Rose) Jawad, Seigler & Ebinger comb. nov. - Senegalia durangensis Britton & Rose, N. Amer. Fl. 23:112. 1928. - TYPE: Mexico, Durango, San Ramon, 21 April-18 May 1906, E.Palmer 107 (holotype: NY!, MEXU photo!, isotypes: F!, MO!, UC!, US!).
Shrub or small tree to 5 m tall. Bark of main trunk dark gray, shallowly fissured. Twigs light brown, not flexuous, puberulent. Short shoots absent. Leaves alternate, 65-160 mm long. Stipules herbaceous, light brown, narrowly triangular, to 2.5 x 0.7 mm near the base, puberulent, persistent. Petiole adaxially grooved, 30-50 mm long, puberulent and with erect hair to 0.2 mm long; petiolar gland solitary, located near the middle of the petiole, sessile, elliptical, 1.1-2.2 mm across, apex irregularly raised, glabrous. Rachis adaxially grooved, 50-130 mm long, puberulent and usually with minute purple glands, a sessile, flattened gland, 0.4-0.8 mm across, between the pinnae of the upper 1 to 2 pinna pairs. Pinnae 6 to 13 pairs per leaf, 60-85 mm long, 8-14 mm between pinna pairs. Petiolules 2.5-4.0 mm long. Leaflets 28 to 36 pairs per pinna, opposite, 1.3-2.1 mm between leaflets, linear, 5.0-7.5 x 1.3-2.1 mm, loosely pubescent on both surfaces with appressed hairs, commonly purplish above, light green to purplish-green beneath, lateral veins obvious, a midvein and 1 to 2 smaller veins from the base, base oblique, margins ciliate, apex obtuse to acute. Inflorescence a loosely flowered cylindrical spike 60-120 mm long, solitary (rarely 2) from the leaf axil, or rarely in short racemose clusters. Peduncle 5-15 x 1.0-1.8 mm, puberulent. Involucre absent. Floral bracts linear, to 1 mm long, pubescent, early deciduous. Flowers sessile, creamy-white; calyx 5-lobed, 1.0-1.4 mm long, densely appressed pubescent; corolla 5-lobed, 2.0-2.5 mm long, densely appressed pubescent; stamen filaments 5.5-7.5 mm long, distinct; ovary glabrous, on a stipe to 0.4 mm long. Legumes dark reddish brown, straight, flattened, not constricted between the seeds, oblong, 80-120 x 16-22 mm, cartilagious, transversely striate, glabrous to lightly puberulent, eglandular, dehiscent along both sutures; stipe to 10 mm long; apex acuminate and usually beaked. Seeds not seen. Flowers: April-June. Chromosome number: Not determined.
Thorn scrub forests and dry thickets, 1600 to 2200 m elevation in the state of Chihuahua and Durango, Mexico.
Few specimens of Mariosousa durangensis are available for study; we saw the type and two others. This is the only species of this genus known from Durango, and it occurs in a region that has been poorly collected. Superficially, M. durangensis is similar to M. mammifera, the leaflets being purplish above, light green beneath, with obvious veins and loosely pubescent on both surfaces with appressed hairs. Leaves with 6-13 pinna pairs, pinnae with 28-36 leaflets, and the sessile petiolar gland that is elliptical in outline and with a raised apex separate this taxon from M. mammifera. The petiolar gland is the most distinctive feature of M. durangensis. Other species of this group have a flat or doughnut- or torus-shaped gland, or the gland is stalked. In M. durangensis, in contrast, the sessile gland appears as an elliptical mound, with a few indentations. On herbarium specimens, this gland has a purple color, and rarely a few long hairs on its surface.
Though none were observed on the few specimens available, it is possible that plants of Mariosousa durangensis occasionally may have prickles. If present, this would suggest that M. durangensis is more closely related to Senegalis macilenta and other members of that genus that commonly have prickles. Also, the petiolar gland of M. durangensis is similar to those found in many members of Senegalia.
- N side of Rio Urique between El Tejeban and Rio Urique, Mpio. Urique, alt. 1600 m, 28 May 1984, Bye, Davis, Randolph & Gerson 12774 (MEXU);
- El Pino 20 km de el entronque a Sapioris, con la Brecha Coyotes-San Miguel de Cruces, Mpio. Tayoltita, lat. N 24o31' y long. W 105o49', alt. 1860 m, 8 Jul 1984, P.Tenorio, C.Romero & T.P.Ramamoorthy 6323 (TEX).