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Name

Vachellia farnesiana (Linnaeus) Wight & Arnott var. minutum (M. E. Jones) Seigler & Ebinger, Phytologia 87:157. 2005.
syn. Acacia farnesiana (L.) Willd. subsp. minuta (M. E. Jones) Ebinger & Seigler, Southw. Naturalist 47:90. 2002.

Synonymy and types

Basionym:  Pithecellobium minutum M. E. Jones, Contr. W. Bot. 18:38. 1933. - Acacia minuta (M. E. Jones) R. M. Beauch., Phytologia 46:5. 1980. - Acacia farnesiana (L.) Willd. subsp. minuta (M. E. Jones) Ebinger & Seigler, Southw. Naturalist 47:90. 2002. - TYPE: MEXICO. BAJA CALIFORNIA: Cacachilla Mts., 2 Oct 1930, M.E.Jones 27265 (holotype: POM-RSA).

Formal description


Large shrub to small tree 8 m tall. Bark dark gray to brown, furrowed. Twigs dark reddish brown to dark gray, slightly flexuous, usually glabrous. Short shoots commonly present above the stipular spines, to 10 mm long, covered with acuminate stipules and old leaf bases. Leaves alternate, also commonly clustered on the short shoots, mostly 15-30 mm long. Stipular spines light to dark brown, usually becoming light gray with age, symmetrical, terete, straight, stout, to 35(55) x 1.5 mm near the base, mostly glabrous. Petiole adaxially grooved, 6-15 mm long, usually densely pubescent with erect hairs; petiolar gland solitary, usually located medially on the petiole, sessile to short stalked, circular to slightly elongated, 0.2-1.0 mm long, apex depressed, glabrous. Rachis adaxially grooved, 10-55 mm long, usually sparsely pubescent with erect hairs, a sessile, circular gland, 0.2-0.4 mm across, between the upper 1 to 2 pinna pairs. Pinnae 2 to 4(5) pairs per leaf, 15-20 mm long, 2-12(16) mm between pinna pairs. Petiolules 0.5-2.0 mm long. Leaflets 8 to 19 pairs per pinna, opposite, 0.5-2.0 mm between leaflets, oblong, 3.0-6.3 x 0.5-1.7 mm, pubescent beneath, lateral veins usually obvious, only one vein from the base, base oblique, margins usually not ciliate, apex broadly acute to obtuse. Inflorescence a densely flowered globose head, 6-10 mm across, solitary or in clusters of 2 to 5 on the short shoots. Peduncles 12-36(45) x 0.2-0.7 mm, lightly puberulent. Involucre 4- to 5-lobed, located at the base of the globose head, glabrous to lightly puberulent, persistent. Floral bracts spatulate, 0.8-1.3 mm long, apex puberulent, deciduous. Flowers sessile, bright yellow; calyx 5-lobed, 1.1-1.8 mm long, glabrous or nearly so; corolla 5-lobed, 1.9-2.8 mm long, glabrous or nearly so; stamen filaments 3.5-5.5 mm long, distinct; ovary glabrous to puberulent, on a stipe to 0.2 mm long. Legumes dark brown to black, straight to slightly curved, nearly terete in cross section, not constricted between the seeds, oblong, 100-170 x 9-18 mm, coriaceous, reticulately striate, glabrous, eglandular, indehiscent; stipe to 7 mm long; apex obtuse to acuminate, sometimes beaked. Seeds uniseriate, imbedded in a sweet pulp, olive green to dark brown, ovoid to ellipsoid, slightly flattened, 4.2-8.0 x 3.5-5.8 mm, smooth; pleurogram U-shaped to oval, 2.5-4.5 mm across. Flowers from December to May. Chromosome number: Not determined.

Distribution

Chaparral, dry thorn -scrub and disturbed habitats from sea level to 1500 m from southern California (San Diego Co.) south through Baja California, Mexico.

Additional info

Vachellia farnesiana var. minuta has a very restricted range in Baja California of Mexico and adjacent California, where it is sympatric with V. farnesiana var. farnesiana. Fruit length in excess of 100 mm, and the uniseriate seeds consistently separate it from the other subspecies of V. farnesiana. Also, its erect habit, being a large shrub or small tree, separates it from V. farnesiana var. pinetorum, a nearly prostrate to weakly erect shrub to 1.5 m tall, that is restricted to southern Florida. Besides fruit characteristics, the larger leaflets separate this taxon from V. farnesiana var. pinetorum, while the usually few pinnae pairs, and the shorter pinna (mostly less than 20 mm long) are helpful in separating this subspecies from V. farnesiana var. farnesiana. The only completely reliable characteristic however is the longer, uniseriate fruits.

Herbarium labels indicate that Vachellia farnesiana var. minuta is mostly associated with arroyos, and other areas where water sometimes accumulated.  Also, it is associated with disturbances, and most populations from San Diego Co., California are from roadsides and other disturbance sites. It is very possible that its occurrence in California is the result of past introductions, probably before the time of settlement by Europeans. Of the more than 40 specimens examined for cyanogenic glycosides, all gave a negative reaction even after the addition of emulsin.

Flowering time

December - May.

Representative specimens

UNITED STATES:

California:

San Diego Co.:

MEXICO:

Baja California:

Baja California Sur:

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