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Name

Mariosousa sericea (Martens & Galeotti) Seigler & Ebinger

Synonymy and types

Acacia sericea Martens & Galeotti, Bull. Acad. Roy. Sci. Bruxelles 10(2):311. 1843. - Senegalia sericea (Martens & Galeotti) Britton & Rose, N. Amer. Fl. 23:111. 1928. - TYPE: Mexico, Puebla, Tehuacan, alt. 6000 ft., May 1840, H.Galeotti 3345 (holotype: BM!, isotypes: K!, P!, MICH photo!, NY photo!).

Acacia pueblensis Brandegee, Univ. California Publ. Bot. 4:85. 1910. - TYPE: Mexico, Puebla, Cerro de Solunte, alt 7-8000 ft., June 1909, C.A.Purpus 3863 (holotype: UC!, MEXU photo!, isotypes: BM!, MO!, NY!, US!).

Formal description

Shrub or small tree 3 to 4 (6) m tall. Bark dark gray, cracked and fissured, breaking away and leaving dark purplish brown, smooth areas.  Twigs dark brown to purplish-brown, not flexuous, glabrous to lightly pubescent.  Short shoots absent.  Leaves alternate, 30-120 mm long. Stipules herbaceous, light brown, narrowly linear, to 4 x 0.4 mm near the base, glabrous to pubescent, sometimes tardily deciduous.  Petiole adaxially grooved, 10-30 mm long, densely pubescent with erect hairs and scattered minute purple glands; petiolar gland solitary, located along the upper half of the petiole, sessile, circular to elliptic, 0.6-1.2 mm long, saucer-shaped to cup-shaped, glabrous, sometimes absent.  Rachis adaxially grooved, 15-100 mm long, pubescent with erect hairs and scattered minute purple glands, a sessile, saucer-shaped gland, 0.5-1.1 mm across, between the pinnae of the upper 1 to 2 pinna pairs.  Pinnae 5 to 13 pairs per leaf, 25-49 mm long, 4-8 mm between pinna pairs.  Petiolules 1.5-2.1 mm long.  Leaflets 14 to 35(44) pairs per pinna, opposite, 0.7-1.3 mm between leaflets, linear, 2.5-5.0 x 0.8-1.5 mm, pubescent on both surfaces with appressed to erect hairs, lateral veins obvious, only one vein from the base, base oblique, margins ciliate, apex acute to obtuse.  Inflorescence a densely flowered cylindrical spike 30-80 mm long, solitary from the leaf axil. Peduncle 3-20 x 0.7-1.2 mm, densely pubescent with erect hairs.  Involucre absent.  Floral bracts linear, to 3.5 mm long, densely pubescent, deciduous.  Flowers sessile, creamy white; calyx 5-lobed, 1.5-2.2 mm long, densely pubescent with erect hairs; corolla 5-lobed, 2.0-3.0 mm long, densely pubescent with erect hairs; stamen filaments 6-8 mm long, distinct; ovary glabrous, on a stipe to 0.3 mm long.  Legumes light yellowish-brown, straight, flattened, not constricted between the seeds, oblong, 90-170 x 15-24 mm, cartilaginous, transversely striate, pubescent, eglandular but usually with minute purple glands when young, dehiscent along both sutures; stipe to 14 mm long; apex acuminate and apiculate to 5 mm long.  Seeds uniseriate, no pulp, dark purplish brown, nearly circular, strongly flattened, 5.0-8.5 mm across, smooth; pleurogram U-shaped, 1.5-2.5 mm across.   Flowers: February-June.  Chromosome number: Not determined.

Distribution

Rocky desert and dry thorn scrub forests from 1100 to 2000 m elevation in Puebla and Oaxaca, Mexico.

Additional info

A small tree, mostly less than 3 or 4 m tall, Mariosousa sericea as known from southeastern Puebla and adjacent Oaxaca.  It occurs at higher elevation, usually above 1100 m elevation, in desert and thorn scrub forests.  Most collections are from roadsides, usually in dry, disturbed habitats, and many are from the Tehuacán valley (Rico Arce and Rodriguez 1998).  Based on the number of specimens available for study, this taxon is not a common component of the vegetation.

Mariosousa sericea is distinct from most other members of the genus; the dense, erect pubescence on most parts of the plant makes it easy to distinguish this taxon.  The leaf rachis, the pinna rachis, and usually the petiole are densely pubescent with erect hairs that exceed 0.3 mm in length.  The leaflets are mostly pubescent with erect to slightly appressed pubescence, while the mature fruits are short pubescent.  Also, the calyx and corolla are pubescent with erect hairs, as are the floral bracts, which are longer than those found in other members of Mariosousa.

Mariosousa sericea possibly hybridizes with M. acatlensis in areas where they are sympatric.  Occasional specimens were encountered with reduced pubescence and many leaflet pairs per pinna, characteristics of M. acatlensis.

Flowering time

February-June.

Representative specimens

MEXICO:

Oaxaca:

Puebla:

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