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Name

Mariosousa compacta (Rose) Seigler & Ebinger

Synonymy and types

Acacia compacta Rose, Contr. U. S. Natl. Herb. 8:31. 1903. - Senegalia compacta  (Rose) Britton & Rose, N. Amer. Fl. 23:111. 1928. - TYPE: Mexico, Oaxaca,  Tomellin Canon, 24 June 1899, J.N.Rose & W.Hough 4680 (holotype: US!,  isotypes: GH!, K!, NY!).

 Lysiloma standleyana Britton & Rose, N. Amer. Fl. 23:81. 1928. - TYPE:  Mexico, Oaxaca, Tomellin, Sept. 1905, J.N.Rose 10082 (holotype NY!, F  photo!, MO photo!).

Formal description

Shrub or small tree to 4 m tall. Bark dark gray, flaking-off in thin strips.  Twigs light brown to dark reddish brown, slightly flexuous, pubescent to glabrous, when young with minute purple glands.  Short shoots commonly present above the nodes, to 3 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 5-30 mm long. Stipules herbaceous, light brown, narrowly linear, to 3 x 0.4 mm near the base, usually glabrous, persistent.  Petiole adaxially grooved, 2.5-14.0 mm long, usually pubescent and with minute purple glands; petiolar gland solitary, located at or just below the lower pinnae pair, sessile, circular, 0.4-1.1 mm across, doughnut-shaped, glabrous.  Rachis adaxially grooved, 0-20 mm long, usually pubescent and with minute purple glands, a sessile, saucer-shaped gland, 0.2-0.6 mm across, occasionally present between the upper pinna pair.  Pinnae 1 to 6 pairs per leaf, 6-18 mm long, 2-5 mm between pinna pairs.  Petiolules 0.5-1.1 mm long.  Leaflets 9 to 22 pairs per pinna, opposite, 0.5-0.9 mm between leaflets, oblong, 1.4-3.0 x 0.5-0.9 mm, glabrous above, usually lightly pubescent beneath with long hairs, lateral veins not obvious, only one vein from the base, base oblique, margins usually ciliate, apex acute to obtuse.  Inflorescence a loosely flowered cylindrical spike 30-70 mm long, solitary (rarely 2 to 3) from the leaf axil. Peduncle 6-13 x 0.4-0.7 mm, usually pubescent and with minute purple glands.  Involucre absent.  Floral bracts linear, to 1.5 mm long, pubescent, early deciduous.  Flowers sessile, creamy-white; calyx 5-lobed, 1.1-1.7 mm long, densely appresses pubescent; corolla 5-lobed, 2-3 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 light yellowish-brown, straight, flattened, not constricted between the seeds, oblong, 50-120 x 10-16 mm, cartilagious, transversely striate, glabrous, eglandular, dehiscent along both sutures; stipe to 8 mm long; apex acuminate and usually beaked.  Seeds uniseriate, no pulp, purplish brown, near circular, strongly flattened, 5-8 mm across, smooth; pleurogram U-shaped, 1.3-2.2 mm across.   Flowers: April-July.  Chromosome number: Not determined.

Distribution

Thorn-scrub forests, thickets, rocky slopes and washes between 500 and 1600 m elevation in the states of Puebla and Oaxaca, Mexico.

Additional info

Mariosousa compacta, a much-branched shrub that rarely exceeds 3m, has a very restricted distribution, occurring in southeastern Puebla and adjacent Oaxaca.  Even there it does not appear to be a common species, relatively little material being available for study.  All material examined is from xeric habitats, usually on rocky slopes and in washes, were M. compacta forms small thickets (Rico Arce and Rodriguez 1998).  The short shoots at many of the nodes, small leaflets (mostly less than 2.5 mm long), leaves that are less than 30 mm (mostly less than 20 mm) long, and fruits with the apex acuminate and beaked, separates M. compacta from other members of this genus. The presence of short shoots is probably an adaptation to xeric conditions.

Mariosousa compacta shows variation with regard to several important characteristics.  Leaf size is highly variable; the leaves that develop on the short shoots are usually smaller and have shorter petioles and fewer pinna pairs, whereas the leaves that form on fast growing shoots are larger; the petioles sometimes reaching a length of 14 mm and with 5-6 pinna pairs developing along the rachis.  The shape and structure of the petiolar gland is also somewhat variable.  The majority of the specimens have a sessile petiolar gland that is doughnut- or torus-shaped, although a few specimens have a stalked petiolar gland with a bulbous apex.  Generally, these glands are found on young leaves forming on the short shoots; other leaves of the specimen have sessile, torus-shaped glands.  It is possible that Mariosousa compacta may rarely hybridize with M. mammifera, the only other species of this group with stalked petiolar glands.

Flowering time

April-July.

Representative specimens

MEXICO:

Oaxaca:

Puebla:

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