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Mariosousa millefolia - pods

Mariosousa millefolia - habit

Name

Mariosousa millefolia (S. Watson) Seigler & Ebinger

Synonymy and types

Acacia millefolia S. Watson, Proc. Amer. Acad. Arts 21:427. 1886. - Senegalia millefolia (S. Watson) Britton & Rose, N. Amer. Fl. 23:111. 1928. - TYPE: Mexico, Chihuahua, Hacienda San Jose, near Batopilas, Aug. 1885, E.Palmer 45 (holotype: GH!, isotypes: MEXU!, NY!).

Formal description

Shrub or small tree to 3 m tall. Bark gray, smooth when young, becoming fissured into square plates 1-2 cm across.  Twigs light brown to greenish brown, not flexuous, usually lightly puberulent.  Short shoots absent.   Leaves alternate, 60-230 mm long. Stipules herbaceous, light brown, narrowly linear, to 6.5 x 0.5 mm near the base, usually glabrous, persistentPetiole adaxially grooved, 30-75 mm long, usually glabrous; petiole gland absent.  Rachis adaxially grooved, 50-190 mm long, glabrous to lightly pubescent; a stalked gland with a globose apex, 0.3-0.9 mm across, between the pinnae of the upper 1 to 2 pinna pairs.  Pinnae (2)6 to 14 pairs per leaf, 30-55 mm long, 10-28 mm between pinna pairs.  Petiolules 2.0-4.0 mm long.  Leaflets 20 to 35(37) pairs per pinna, opposite, 0.8-1.6 mm between leaflets, oblong, 2.0-6.5 x 0.7-1.4 mm, glabrous above, lightly pubescent beneath with appressed hairs, lateral veins not obvious, only one vein from the base, base oblique, margins sometimes ciliate, apex acuminateInflorescence a loosely flowered cylindrical spike 30-75 mm long, solitary (rarely 2 to 3), from the leaf axil. Peduncle 5-15 x 0.3-0.8 mm, glabrous to lightly puberulent.  Involucre absent.  Floral bracts linear, to 1.3 mm long, glabrous to lightly pubescent, early deciduous.  Flowers sessile, creamy-white; calyx 5-lobed, 1.1-1.6 m long, glabrous; corolla 5-lobed, 2.0-2.7 mm long, glabrous; stamen filaments 4.5-6.5 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, 70-170 x 12-21 mm, chartaceous, irregularly striate, glabrous, eglandular, dehiscent along both sutures; stipe to 12 mm, apex acute to obtuse.  Seeds uniseriate, no pulp, dark brown, nearly circular, strongly flattened, 6.2-9.5 mm across, smooth; pleurogram U-shaped, 2-3 mm across.   Flowers: June-August.  Chromosome number: Not determined.

Distribution

Desert grasslands, rocky slopes, subtropical scrub, and open oak woodlands from 700 to 1700 m elevation in southern Arizona, south through Sonora to western Chihuahua, Mexico.

Additional info

A shrub to small tree, usually less than 2 m tall, Mariosousa millefolia is relatively common in desert grassland and desert scrub vegetation in extreme southern Arizona and adjacent Sonora, Mexico.  Commonly collected along the steep sides and floors of canyons, M. millefolia is rarely a dominant member of the vegetation, most collections indicating scattered individuals. Though numerous specimens are available from throughout most of the geographic range of this taxon, no specimens, other than the type collection, is known from Chihuahua.  This taxon may be extremely rare in southwestern Chihuahua, or it is possible that the collecting data on the type specimens is incorrect.  This collection, which was designated as the lectotype by Isley (1969), is more than 100 km east of any specimens of M. millefolia seen by the present authors.

Mariosousa millefolia is distinct from other members of this genus, as it lacks a petiolar gland and possess a stalked rachis gland between the upper pairs of pinnae.  The only other taxa of this group within the range of M. millefolia, are M. willardiana and M. russelliana.  Mariosousa millefolia is easily distinguished from M. willardiana, which has papery, exfoliating bark and leaves with only 1-3 pinnae pairs.  Leaflets with appressed hairs, the stalked rachis glands, and the persistent stipules of M. millefolia separate it from M. russelliana.  In addition, M. millefolia is normally a shrub found above 700 m elevation, the other species are trees and commonly occur at lower elevations.

Flowering time

June-August.

Representative specimens

MEXICO:

Sonora:

UNITED STATES:

Arizona:

Cochise Co.:

Pima Co.:

Santa Cruz Co.:

New Mexico:

Hidalgo Co.:

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