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Vachellia bilimekii - bark

Vachellia bilimekii - hanging seed

Vachellia bilimekii - scene

 

Vachellia bilimekii - stem

Name

Vachellia bilimekii (Macbride) Seigler & Ebinger, Phytologia 87:  145.  2005.
syn. Acacia bilimedii Macbride, Contr. Gray Herbarium 59:  6.  1919.

Synonymy and types

Basionym:  Acacia bilimekii J. Macbr., Contr. Gray Herb. 59: 6.  1919.  Acaciopsis bilimekii (J. Macbr.) Britton & Rose, N. Amer. Fl.  23: 94.  1928. - TYPE:  MEXICO.  MORELOS:  Cuernavaca, 10 Jan 1866, D. Bilimek 128 (holotype: GH).

Acacia ambigua Rose, Contr. U. S. Natl. Herb.  8: 31. 1903. - TYPE:  MEXICO.  PUEBLA:  on the hills above Matamoras, where it is common, 26 Jun 1899, J. N. Rose & W. Hough 4698 (holotype:  US).  NOTE:  Not Acacia ambigua Hoffannsegg (1826), which is based on a sterile specimen from Senegal, the identity of which is unknown (Ross 1979).  Not Acacia ambigua Vogel (1836), a species from the Caribbean with prickles and lacking stipular spines, which is a synonym of Acacia vogeliana Steud. (Britton and Rose 1928).

Acacia sericocarpa Rose, Contr. U. S. Natl. Herb.  8: 300.  1905. -TYPE:  MEXICO.  PUEBLA:  on the hills above Matamoras, where it is common, 26 Jun 1899, J. N. Rose & W. Hough 4698 (holotype:  US).  NOTE:  Not Acacia sericocarpa Fitzgerald (1904), a phyllodinous acacia species from Western Ausralia (Maslin, 2001b).

Formal description

Tree to 7(12) m tall.  Bark dark gray to brown, shallowly furrowed.  Twigs dark purplish brown to dark gray, slightly flexuous, usually densely pubescent.  Short shoots commonly present above the stipular spines, to 6 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 0.3-5.0 mm long.  Stipular spines dark brown to gray, symmetrical, terete, straight, thin, to 20(40) x 2 mm near the base, glabrous to lightly puberulent.  Petiole adaxially grooved, 0.3-3.0(5) mm long, pilose; petiolar gland solitary, located between the pinna pair, sessile, circular, 0.3-1.3 mm across, apex depressed, glabrous, sometimes absent.  Rachis absent.  Pinnae 1 pair per leaf, 1-15 mm long.  Petiolules 1-6 mm long.  Leaflets 1 to 2(3) pairs per pinna, opposite to subopposite, 2-8 mm between leaflets, oblong to elliptic, 6-27 x 2-10 (13)mm, usually pubescent on both surfaces, lateral veins obvious, 3 to 5 veins from the base, base oblique, margins ciliate, apex obtuse and usually mucronate.  Inflorescence a loosely flowered elongated spike, 15-50 mm long, solitary or in clusters of 2 to 4 on the short shoots.  Peduncles 0-3 x 0.5-0.8 mm, puberulent.  Involucre usually 4-lobed, at the base of the peduncle, usually glabrous, persistent.  Floral bracts spatulate, 0.4-0.8 mm long, puberulent, deciduous.  Flowers sessile, white to cream-colored; calyx 4-lobed, 0.8-1.1 mm long, nearly glabrous; corolla 4-lobed, 1.1-1.5 mm long, glabrous or nearly so; stamen filaments 2.7-3.7 mm long, distinct; ovary glabrous, on a stipe to 0.3 mm long. Legumes dark reddish brown, straight to slightly curved, flattened, constricted between the seeds, linear, 60-100 x 4-7 mm, coriaceous, reticulately striated, lightly to densely pilose, eglandular, dehiscent; a chartaceous pericarpic strip lining each valve stipe 7-14 mm long; apex acuminate and sometimes beaked.  Seeds uniseriate, no pulp, brown to gray brown, oblong, strongly flattened, 6.8-8.7 x 3.5-4.5 mm, smooth; pleurogram oblong to U-shaped, 1-2 mm across. Flowersin December to April. Chromosome number:  Not determined.

Distribution

In open pastures, along roadsides, and other disturbed sites between 1000 and 2200 m in the states of Morelos, Oaxaca, and Puebla, Mexico.

Additional info

Some confusion exists as to the correct name of this taxon, A. amentacea DeCandolle (1825) sometimes being proposed. The description by DeCandolle, however, does not fit all of the characteristics of V. bilimekii, particularly the pubescent leaflets.  According to McVaugh (1986) the type of A. amentacea is a painting, represented by De Candolle's plate no. 208.  This plate is a copy from the original made by the artists of the Sessé and Mociño expedition (Anonymous 1981).  The species represented by this drawing is probably what is now being called V. bilimekii, but without a specimen no accurate determination can be made (Lee et al. 1989).

Vachellia bilimekii is the only taxon of this group that commonly has only one pair of leaflets on most pinnae.  Two pairs of leaflets are found on some pinnae of most specimens, and rarely 3 pairs of leaflets are present.  Generally, the primary leaves (those developing from the nodes between the stipular spines) have 2 pairs of leaflets on many pinnae, whereas the leaves developing from the short shoots commonly have one pair of leaflets per pinna.  Also, the primary leaves usually have a shorter petiole (to 2 mm long), the petiole is thicker and more densely pubescent, the petiolar gland is commonly larger (to 1 mm across) and the pinnae are longer (to 15 mm long).  Short shoot leaves, in contrast, commonly have petioles that may get to 5 mm long, are thinner and lightly pubescent, whereas the petiolar gland is usually 0.3-0.6 mm across and the pinnae rarely exceed 8 mm in length.

The short petiole, the fact that many of the leaves have only one pair of pinnae, and the relatively large oblong to elliptic leaflets separates V. bilimekii from other members of this group.  Also, most specimens of V. bilimekii have a dense cluster of leaves on the short shoots, whereas these are usually absent in V. pringlei.  Additionally, V. pringlei has obvious striations on the calyx which are absent in V. bilimekii.  As is typical of all members of this group, only a few specimens of V. bilimekii tested positive for cyanide production (Lee et al. 1989).

Flowering time

December-April.

Representative specimens

MEXICO:

Morelos:

Oaxaca:

Puebla:

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