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Vachellia glandulifera

Vachellia glandulifera

Name

Vachellia glandulifera (S. Watson), Seigler & Ebinger, Phytologia 87:  152.  2005.
syn.  Acacia glandulifera S. Watson, Proc. Amer. Acad. Arts  25:  147.  1890.

Synonymy and types

Basionym:  Acacia glandulifera S. Watson, Proc. Amer. Acad. Arts  25: 147.  1890.  Poponax glandulifera (S. Watson) Britton & Rose, N. Amer. Fl.  23: 88.  1928. - TYPE:  MEXICO.  COAHUILA:  limestone hills, Carneros Pass, 7 Sep 1889, C. G. Pringle 2861 (holotype:  GH; isotypes: F, NY, VT).  NOTE:  Not Acacia glandulifera Schinz (1900) which is considered a synonym of Acacia nebrownii Burtt Davy, a species with stipular spines from Africa (Ross 1979).

Formal description

Shrub to 2 m tall.  Bark dary gray, smooth.  Twigs dark reddish brown to gray, not flexuous, lightly appressed puberulent, sometimes slightly glutinous and with dark purple, sessile glands.  Short shoots commonly present above the stipular spines, to 3 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also clustered on the short shoots, 2-9 mm long.  Stipular spines reddish brown, becoming light gray with age, symmetrical, terete, slightly recurved, stout, to 17 x 1.3 mm near the base, glabrous to lightly puberulent.  Petiole adaxially shallowly grooved, 2-5(7) mm long, lightly puberulent; petiolar gland solitary, located between to just below the lower pinna pair, sessile, circular, 0.2-0.4 mm across, doughnut-shaped, glabrous.  Rachis adaxially shallowly grooved, 0-7 mm long, puberulent, a sessile, doughnut-shaped gland 0.1-0.3 mm across between the upper pinna pair.  Pinnae 1 to 2(3) pairs per leaf, 4-9 mm long, 1-4 mm between pinna pairs.  Petiolules 0.4-1.2 mm long.  Leaflets 4 to 9 pairs per pinna, opposite to subopposite, 0.6-1.2 mm between leaflets, elliptic to oval, 1.8-3.0 x 0.7-1.0 mm, mostly glabrous, lateral veins not obvious, only one vein from the base, base oblique, margins usually ciliate, apex obtuse.  Inflorescence a densely flowered globose head, 6.5-9.0 mm across, solitary or in small clusters of 2 to 5 on the short shoots.  Peduncles 9-20 x 0.4-0.6 mm, lightly puberulent.  Involucre bracts 4 to 7, scattered near the middle of the peduncle, lightly puberulent, usually early deciduous.  Floral bracts spatulate, 0.9-1.4 mm long, lightly puberulent, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 0.8-1.1 mm long, glabrous or nearly so; corolla, 5-lobed, 1.7-2.2 mm long, glabrous or nearly so; stamen filaments 3.3-4.5 mm long, distinct; ovary glabrous and glandular, sessile or on a stipe to 0.2 mm long.  Legumes dark reddish-brown, straight to slightly curved, flattened, more or less constricted between the seeds, linear, 40-95 x 4.8-7.5 mm, chartaceous, not reticulately striate, glabrous and glutinous, covered with numerous dark reddish brown glands to 0.3 mm across and with stalks to 1.0 mm long, dehiscent; a chartaceous pericarpic strip lining each valve; stipe to 6 mm long; apex acuminate and usually beaked.  Seeds uniseriate, no pulp, mottled gray-brown, oblong, strongly flattened, 4.5-7.5 x 3.0-5.8 mm, smooth; pleurogram U-shaped, 0.6-0.9 mm across. Flowers in March to July. Chromosome number: 2n = 26 (Parfitt 1979).

Distribution

Locally common on limestone hills at higher elevations (1000-2400 m) in the Chihuahuan Desert of Mexico in the states of Chihuahua, Coahuila, Durango, Nuevo León and Zacatecas.

Additional info

Vachellia glandulifera is very distinct; its identification is straightforward with the use of several characters, fruit characters being the most salient.  The combination of numerous stalked glands, inflated valve sutures, and the dark brown color separates the fruits of this species from all closely related species.  Also, the short (mostly less than 5 mm long) broad petioles, and whitish, recurved spines help identify this species.  Specimens are variable with regard to only a few characters.  Commonly, most vegetative parts of the plant are sparsely puberulent, but densely puberulent individuals are occasionally found.  The petioles are mostly less than 5 mm long, but rarely longer petioles are found.  Also, most leaves have only a single pair of pinnae, particularly the leaves developing from the short shoots.  The primary leaves, on the occasional fast growing twigs, will sometimes have 2, or rarely 3 pairs of pinnae.  The general lack of variation, as well as its relatively restricted range indicates that this species does not hybridize with other members of the group.  Some specimens (38%) tested were cyanogenic, mostly giving a weak reaction.

A species restricted to higher elevations in the Chihuahuan Desert of north central Mexico, Vachellia glandulifera was once considered very rare, being restricted to the type locality (Britton and Rose 1928).  Parfitt (1979) mentions collections from Chihuahua, Coahuila, Durango, and Zacatecas; more recently it has been found in Nuevo León, and may have a distribution even greater than the states listed.  Where found, this species commonly forms extensive thickets, having a preference for calcareous soils.  Unlike the other species of this group, V. glandulifera is generally restricted to slopes and hilltops, rarely being found on plains or washes.  Many individuals are less than 1 m tall, but larger size is attainable.  Most plants are heavily browsed.

This species is sympatric with both Vachellia constricta and V. vernicosa (syn. A. neovernicosa), but there is no evidence to suggest that hybridization occurs with either of these taxa.  Though morphologically similar to V. vernicosa, no specimens with intermediate characteristics were encountered.  A PCA in which this species was analyzed with other members of the V. constricta group indicated that V. glandulifera is morphologically distinct.

Flowering time

March - July.

Representative specimens

MEXICO:

Chihuahua:

Coahuila:

Durango:

Nuevo León:

Zacatecas:

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