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Name

Vachellia vernicosa (Britton & Rose), Seigler & Ebinger, Phytologia 87:  169.  2005.
syn.  Acacia neovernicosa Isely, Sida 3:  380.  1969.

Synonymy and types

Basionym:  Acaciopsis vernicosa Britton & Rose, N. Amer. Fl.  23: 96.  1928.  Acacia vernicosa Standl. , Cont. U. S. Natl. Herb.  20: 187.  1919 (nom. Illeg.).  Acacia constricta Benth. var. vernicosa L. Benson, Amer. J. Bot.  30: 238.  1943.  Acacia neovernicosa Isely,  Sida 3:380. 1969.  (based on the same type). -  TYPE:  MEXICO.  CHIHUAHUA:  in the vicinity of Santa Rosalía, alt. 1200 m, 13-15 Jun 1908, E. J. Palmer 385 (holotype:  US; isotypes:  GH, MO, NY).  NOTE:  Not Acacia vernicosa Fitzgerald (1904), an Australian species with phyllodes, presently considered a synonym of Acacia incrassata Hook. (Maslin 2001c).

Formal description

Shrub to 3 m tall.  Bark dark gray to dark reddish gray, smooth.  Twigs dark reddish brown to dark purple, not flexuous, glabrous and glutinous.  Short shoots commonly present above the stipular spines, to 4 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 3-12 mm long.  Stipular spines dark reddish brown, becoming light gray with age, symmetrical, terete, straight to slightly reflexed, subulate, to 11 (25) x 1 mm near the base, glabrous and sometimes glutinous.  Petiole adaxially shallowly grooved, 3-8 (10) mm long, glabrous and glutinous; petiolar gland solitary, located at or just below the lower pinna pair, sessile, circular, 0.1-0.4 mm across, doughnut-shaped, glabrous.  Rachis adaxially shallowly grooved, 0-9 mm long, glabrous, a small, sessile, doughnut-shaped gland sometimes present between the pinna pairs.  Pinnae 1 to 2 (3) pairs per leaf, 4.5-13.0 mm long, 1-4 mm between pinna pair.  Petiolules 0.5-1.5 mm long.  Leaflets 4 to 12 pairs per pinna, opposite to subopposite, 0.5-1.4 mm between leaflets, elliptic to oval, 1.1-2.7 x 0.5-0.9 mm, glabrous and glutinous, lateral veins not obvious, only one vein from the base, base oblique, margins not ciliate, apex obtuse.  Inflorescence a densely flowered globose head, 6-8 mm across, solitary or in small clusters of 2 to 5 on the short shoots.  Peduncles 10-25 (30) x 0.2-0.4 mm, glabrous and glutinous.  Involucre 4- to 6- lobed, located near the middle of the peduncle, glabrous, usually persistent.  Floral bracts spatulate, 0.7-1.5 mm long, glabrous, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 0.6-1.2 mm long, glabrous; corolla 5-lobed, 1.4-2.1 mm long, glabrous; stamen filaments 2.7-4 mm long, distinct; ovary glabrous, on a stipe to 0.2 mm long.  Legumes reddish-brown, straight to slightly curved, flattened, usually constricted between the seeds, linear, 38-90 x 2.1-3.8 mm, chartaceous, not reticulately striate, glabrous and glutinous, glandular with small, clear to reddish, sessile glands, dehiscent; a chartaceous pericarpic strip lining each valve; stipe to 12 mm long; apex acuminate and usually beaked.  Seeds uniseriate, no pulp, mottled gray-brown, oblong, strongly flattened, 4.5-6.5 x 1.7-3.0 mm, smooth; pleurogram oval to U-shaped, 0.4-0.9 mm across. Flowers in March to September. Chromosome number:  2n = 26 (Turner and Fearing 1960).

Distribution

Common on disturbed, arid sites of slopes and plains in sandy and gravelly calcareous and gypseous soils from 700-1700 m elevation from southwestern Texas to southeastern Arizona, south through the thorn scrub and desert regions of Mexico in the states of Chihuahua, Coahuila, Durango, Querétaro, San Luis Potosí and Zacatecas.

Additional info

Vachellia vernicosa (syn. Acacia neovernicosa) is usually easy to identify, the glutinous and vernicose covering on the leaves, twigs, and fruits, the lack of pubescence, and the 1-2 pairs of pinnae, separate this species from other members of the Vachellia constricta group.  This taxon is consistent in its morphological characteristics throughout most of its range.  Nearly all specimens have 1-2 pinnae pairs per leaf, but occasionally three pairs occur, particularly on the primary leaves that develop between the stipular spines on new growth.  The leaves of the short shoots consistently have one or occasionally two pinna pairs.  Leaflet size is essentially the same on leaves that develop from short shoots and the primary leaves on rapidly growing stems.  All specimens examined have a glutinous covering, giving the plant a shiny appearance.  Rarely, this glutinous covering was extremely thin, requiring magnification to be seen. The glutinous compounds consist mainly of a mixture of flavonoid aglycones (Wollenweber and Seigler 1982).  Also, the leaflets of many specimens have punctate glands, though these are not always obvious.

It has been suggested that hybridization occurs between Vachellia vernicosa and closely related species, particularly in western Coahuila, eastern Chihuahua, and the Trans-Pecos of Texas, where this taxon is sympatric with both V. schottii and V. constricta.  Some specimens collected in Brewster and Presidio Counties, Texas, are intermediate in leaflet characteristics between V. schottii and V. vernicosa and probably are of hybrid origin.  Also, a single probable hybrid between V. constricta and V. vernicosa was observed.

Rarely, Vachellia constricta is confused with V. vernicosa, and originally both were considered within the original concept of V. constricta (Benson 1943, Standley 1919).  The lack of pubescence, glutinous leaves and twigs, and the small number of pinna pairs of V. vernicosa can be used consistently for separation.  Also, specimens of V. constricta are consistently cyanogenic, those of V. vernicosa only rarely so.  In addition, the chromosome numbers differ, V. constricta has 2n = 52, and V. vernicosa 2n = 26.  Vachellia vernicosa frequently prefers gypseous soil, and generally flowers one to two weeks before V. constricta (Turner 1959).  Isely (1969) mentions that these species are not separated geographically, nor apparently ecologically, but he found little evidence of intermediacy.

Clarke et al. (1990) found that Vachellia vernicosa is rarely cyanogenic, only 12% of the specimens tested giving a positive reaction.  Generally, the reaction was weak, indicating that only small amounts of the cyanogenic compound were present.  Occasional specimens gave a strongly positive reaction.  Herbarium specimens from southwestern Texas and adjacent New Mexico gave a consistently negative test for cyanide.  In tests of three populations from Big Bend National Park, of the 90 specimens tested, only one gave a weakly positive reaction.

Flowering time

March - September.

Representative specimens

UNITED STATES:

Arizona:

Cochise Co.:

New Mexico:

Dona Ana Co.:

Eddy Co.:

Texas:

Brewster Co.:

Culberson Co.:

El Paso Co.:

Hidalgo Co.:

Hudspeth Co.:

Jeff Davis Co.:

Pecos Co.:

Presidio Co.:

Reeves Co.:

Terrell Co.:

Val Verde Co.:

MEXICO:

Baja California:

Chihuahua:

Coahuila:

Durango:

Querétaro:

San Luis Potosí:

Sonora:

Tamaulipas:

Zacatecas:

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