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Mariosousa usumacintensis - leaf
Mariosousa usumacintensis
Mariosousa usumacintensis
Mariosousa usumacintensis

Name

Mariosousa usumacintensis (Lundell) Seigler & Ebinger

Synonymy and types

Acacia usumacintensis Lundell, Contr. Univ. Michigan Herb.  4:8. 1940. - TYPE: Mexico, Tabasco, Boca Cerro on the Rio Usumacinta above Tenosique, 1-5 July 1939, E.Matuda 3550 (holotype: MICH!, isotypes: K!, LL!, MEXU!, MICH!, NY!).

Formal description

Tree to 30 m tall. Bark dark gray, shallowly furrowed.  Twigs brown to greenish brown, not flexuous, glabrous to lightly puberulent.  Short shoots absent.  Leaves alternate, 90-200 mm long. Stipules herbaceous, light brown, narrow triangular, to 2.2 x 0.5 mm near the base, glabrous to lightly puberulent, persistent.  Petiole adaxially shallowly grooved, 30-70 mm long, glabrous to lightly puberulent; petiole gland solitary, usually located on the lower third of the petiole, sessile, commonly elliptical, 1-6 mm long, flattened, glabrous.  Rachis adaxially grooved, 50-140 mm long, glabrous to lightly puberulent, a sessile, saucer-shaped gland, 1.0-1.9 mm across, between the upper pinna pair.  Pinnae 7 to 15 pairs per leaf, 55-90 mm long, 5-12 mm between pinna pairs.  Petiolules 1.7-3.0 mm long.  Leaflets (33)36 to 55 pairs per pinna, opposite, 1.0-1.6 mm between leaflets, oblong, 4-7 x 1.2-1.7 mm, glabrous, lateral veins obvious, a midvein and 1 to 3 smaller veins from the base, base oblique, margins ciliate, apex acute to obtuse.  Inflorescence a loosely flowered cylindrical spike 50-110 mm long, 1 to 3 from the leaf axil, or sometimes in terminal racemose clusters. Peduncle 7-15 x 0.7-1.1 mm, puberulent.  Involucre absent.  Floral bracts linear, to 1 mm long, puberulent, early deciduous.  Flowers sessile, creamy-white; calyx 5-lobed, 1.1-1.5 mm long, densely appressed pubescent; corolla 5-lobed, 1.8-2.5 mm long, densely appressed pubescent; stamen filaments 4-6 mm long, distinct; ovary glabrous to lightly pubescent, on a stipe to 0.3 mm long.  Legumes light yellowish-brown to dark brown, straight, flattened, not constricted between the seeds, oblong, 90-250 x 20-33 mm, cartilaginous, transversely striate, glabrous, eglandular, dehiscent along both sutures; stipe to 22 mm long; apex acute.  Seeds uniseriate, no pulp, dark reddish brown, oblong to oval, strongly flattened, 8.8-10.0 x 7.0-9.0 mm, smooth; pleurogram U-shaped, 3-4 mm across.   Flowers: April-June.  Chromosome number: Not determined.

Distribution

Moist tropical forests, along streams, and moist disturbed sites below 500 m elevation in Belize, Guatemala, and the states of Campeche, Chiapas, Oaxaca, Tabasco and Veracruz, Mexico.

Additional info

Mariosousa usumacintensis is a tall tree that is a common component of lowland tropical rain forests in Guatemala and southern Mexico.  The present authors have observed no specimens of this taxon farther south than Guatemala and Belize. Specimens labeled M. usumacintensis from Nicaragua are the result of confusing this taxon with various species of Lysiloma.  Mariosousa usumacintensis specimens are commonly misidentified as L. acapulcensis (Kunth) Benth.  Thompson (1980), in a revision of Lysiloma, annotated the type of M. usumacintensis as L. acapulcensis.  This specimen (E. Matuda 3550), however, is M. usumacintensis, having numerous separate filaments remaining at the base of some of the fruits.

Mariosousa usumacintensis is relatively uniform in its characteristics.  Most specimens are nearly glabrous, but some have puberulent young twigs, petioles and rachises.  Some variation does occur in leaflet size, as well as in the number of leaflets per pinna.  Leaflet pairs vary from 33 to 55 depending on the position of the pinna on the rachis, the pinnae toward the apex and base having fewer leaflet pairs than those near the middle of the rachis.  This species is easily separated from other members of this genus by the relatively large number of pinna pairs (usually more than 8 on most leaves), the large number of leaflets per pinna (usually more than 35), and by the presence of a large (1-6 mm long), sessile petiolar gland with a flattened apex, located along the lower third of the petiole. The large number of pinna pairs, and the petiolar gland easily separates this taxon from M. dolicostachya, to which M. usumacintensis is closely related.

Flowering time

April-June.

Representative specimens

BELIZE:

GUATEMALA:

Izabal:

Petén:

MEXICO:

Campeche:

Chiapas:

Tabasco:

Veracruz:

 

 

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