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Mariosousa coulteri - habit

Mariosousa coulteri

Mariosousa coulteri - flowers

Mariosousa coulteri - leaf

Mariosousa coulteri - habitat

Mariosousa coulteri - bark

Mariosousa coulteri - habit

Name

Mariosousa coulteri (Bentham) Seigler & Ebinger

Synonymy and types

Acacia coulteri Bentham in A. Gray, Pl. Wright. 1:66. 1852. - Senegalia coulteri  (Bentham) Britton & Rose, N. Amer. Fl. 23:112. 1928. - TYPE: Mexico,  Hidalgo, Zimapan, T.Coulter s.n. (holotype: K!,, F photo!, GH photo!, MEXU  photo!, MICH photo!, MO photo!, NY photo!, US photo & fragment!).

Formal description

Shrub or small tree to 15 m tall. Bark dark gray, shallowly furrowed.  Twigs light brown to greenish brown, not flexuous, glabrous to lightly appressed puberulent.  Short shoots absent.  Leaves alternate, 50-150 mm long. Stipules herbaceous, light brown, narrowly linear, to 2.1 x 0.4 mm near the base, glabrous, tardily deciduous.  Petioles adaxially shallowly grooved, 25-55 mm long, usually lightly appressed puberulent; petiole gland solitary, located on the upper third of the petiole and commonly just below the first pinna pair, sessile, nearly circular, 0.5-1.6 mm across, doughnut -shaped, glabrous, rarely absent.  Rachis adaxially shallowly grooved, 20-100 mm long, lightly uberulent, a sessile, cup-shaped gland, 0.4-0.9 mm across, between upper pinna pair.  Pinnae 5 to 11 pairs per leaf, 40-90 mm long, 6-12 mm between pinna pairs.  Petiolules 3-5 mm long.  Leaflets 18 to 35 pairs per pinna, opposite, 1.5-2.3 mm between leaflets, oblong, 4.5-7.5 x 1.4-2.1 mm, glabrous above, lightly appressed pubescent beneath, lateral veins obvious, a midvein and occasionally one other vein from the base, base oblique, margins ciliate, apex broadly acute to obtuse.   Inflorescence a loosely flowered cylindrical spike 50-90 mm long, 1 to 4 from the leaf axil, or rarely in terminal racemose clusters. Peduncle 7-13 x 0.5-1.0 mm, usually puberulent.  Involucre absent.  Floral bracts linear, to 1 mm long, puberulent, early deciduous.  Flowers sessile, creamy-white; calyx 5-lobed, 1.2-1.6 mm long, lightly appressed pubescent; corolla 5-lobed, 1.9-2.6 mm long, lightly appressed pubescent; stamen filaments 5.0-6.5 mm long, distinct; ovary glabrous, on a stipe to 0.4 mm long.  Legumes light yellowish brown to dark brown, straight, flattened, not conscricted between the seeds, oblong, 100-185 x 16-25 mm, cartilagious, transversely striate, glabrous, eglandular, dehiscent along both sutures; stipe to 15 mm long; apex acute to acuminate.  Seeds uniseriate, no pulp, dark reddish brown, circular to nearly oblong, strongly flattened, 7.3-10.5 x 5.5-8.5 mm, smooth; pleurogram U-shaped, 2.2-3.5 mm across.   Flowers: April-August.  Chromosome number: Not determined.

Distribution

Open dry forest, dense thorn scrub thickets, and dry rocky slopes below 1800 m elevation in the foothills and mountains of northeastern Mexico in the states of Coahuila, Guanajuato, Hidalgo, Nuevo León, Querétaro, San Luís Potosí, and Tamaulipas.

Additional info

Abundant in northeastern Mexico, Mariosousa coulteri, is a common component of relatively dry forests and thorn-scrub thickets.  Many of the collections are from roadsides and rocky pastures.  This taxon is abundant in the states of Tamaulipas and San Luís Potosí, becoming less common to the south.  Mariosousa coulteri is similar morphologically to M. russelliana, which is a small shrub or understory tree common in Sonora and parts of Sinaloa.  Mariosousa russelliana has usually been considered a part of this genus, Britton and Rose (1928) being the only authors who recognized the two as distinct.  Both of these taxa have leaves with fewer than 12 pinnae pairs, pinnae with less than 35 leaflet pairs, petiolules that exceed 2.4 mm in length, and identical petiolar glands.  Though similar in many traits, these taxa are easy to separate, M. coulteri having appressed pubescence on the lower leaflet surface, perianth, and the rachis and pinnae rachises; M. russelliana, in contrast, being glabrous throughout.

The only species of this group found within the range of Mariosousa coulteri is M. mammifera, which consistently has leaflets that are purplish and appressed pubescent above, leaves that mostly have less than six pinna pairs, and stalked petiolar glands with a globose apex.  In M. coulteri, the leaflets are not purplish and lack appressed pubescent above, the leaves mostly have more than seven pinna pairs, and the petiolar glands are doughnut-shaped and sessile.

The stipules of Mariosousa coulteri seedlings are somewhat spinescent, but are only weakly rigid after the first leaf stage, and become progressively smaller and less rigid on older plants (Vassal 1972).  Because this species lacks prickles, because of correlations of the cotyledonary petiole and shape, and certain other features, Vassal placed M. coulteri in his subgenus Acacia, a group mostly equivalent to Bentham's (1842) Acacia, series Gummiferae.  However, M. coulteri also differs in some significant features from members of that series.  For example, the pollen grains of M. coulteri are porate, while other members of Bentham's series Gummiferae are colporate (Vassal 1972).

Flowering time 

April-August.

Representative specimens

MEXICO:

 Coahuila:

Guanajuato:

Hidalgo:

Nuevo León:

Queréaro:

San Luís Potosí:

Tamaulipas:

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