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Vachellia constricta - stem

Vachellia constricta - habit

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Vachellia constricta

Name

Vachellia constricta (Bentham), Seigler & Ebinger, Phytologia 87:  152.  2005.
syn.  Acacia constricta Bentham in Gray, Pl. Wright.  1:  66.  1852.

Synonymy and types

Basionym:  Acacia constricta Benth. in Gray, Pl. Wright. 1: 66.  1852.  Acaciopsis constricta (Benth.) Britton & Rose, N. Amer. Fl.  23: 96.  1928. - TYPE:  MEXICO.  CHIHUAHUA:  May-Oct 1849, C. Wright 162 (holotype:  K; isotypes:  GH, NY, US).

Acacia constricta Benth. var. paucispina Wooton & Standl.,  Bull. Torrey Bot. Club 36: 105.  1909.  Acaciopsis constricta (Benth. in Gray) Britton & Rose var. paucispina (Wooton & Standl.) Moldenke, Revista Sudamer. Bot.  4: 15.  1937. -  TYPE:  UNITED STATES.  NEW MEXICO:  Sierra Co., Animas Creek in the Black Range, alt. 1500 ft., 13 Jul 1904, O. B. Metcalfe 1123 (holotype:  US).

Mimosa arcuata M. Martens & Galeotti, Bull. Acad. Roy. Sci. Bruxelles  10: 310.  1843. -  TYPE:  MEXICO.  OAXACA:  se trouve sur le flanc des montagnes calcaires et cactiferes, à l'est de Tehuacan de las Grandas, vers 6,000 pieds.  Fl. jaunes,  H. Galeotti 3222 (holotype:  BR; isotypes:  G, K). (Rudd 1976-1982).  NOTE:  Not Acacia arcuata Sieber ex Sprengel (1826), a taxon with phyllodes that is a synonym of Acacia melanoxylon R. Br. (Cowan and Maslin, 2001).

Formal description

Shrub or small tree to 6 m tall.  Bark dark gray, smooth to shallowly furrowed.  Twigs dark purplish brown to dark reddish brown, not flexuous, glabrous to pubescent.  Short shoots commonly present above the stipular spines, to 3 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 12-35(40) mm long.  Stipular spines reddish brown, usually becoming light gray with age, symmetrical, terete, straight, stout, to 15(38) x 1.2 mm near the base, glabrous to rarely lightly puberulent.  Petiole adaxially grooved, 4-14 mm long, lightly puberulent; petiolar gland solitary, usually located at or just below the lower pinna pair, sessile to rarely stalked, circular, 0.2-0.7 mm across, doughnut-shaped, glabrous.  Rachis adaxially grooved, 6-35 mm long, glabrous to lightly puberulent, a sessile, doughnut-shaped gland, 0.2-0.4 mm across, between the upper pinna pair.  Pinnae 2 to 8 pairs per leaf, 5-12 mm long, 3.5-8.8 mm between pinna pairs.  Petiolules 0.4-1.1 mm long.  Leaflets 5 to 12 pairs per pinna, opposite to subopposite, 0.7-1.5 mm between leaflets, elliptic to oblong or oval, 1.5-3.6 x 0.7-1.3 mm, mostly glabrous, lateral veins not obvious, only one vein from the base, base oblique, margins usually ciliate, apex obtuse to acute.  Inflorescence a densely flowered globose head, 5.5-9.5 mm across, solitary or in small clusters of 2 to 5 on the short shoots.  Peduncles 11-26 x 0.2-0.4 mm, lightly puberulent.  Involucre 4- to 7- lobed or scattered bracts located near the middle of the peduncle, lightly pubescent, usually persistent.  Floral bracts spatulate, 0.9-1.4 mm long, glabrous to lightly puberulent, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 0.9-1.4 mm long, glabrous or nearly so; corolla 5-lobed, 1.7-2.4 mm long, glabrous or nearly so; stamen filaments 3.5-5.0 mm long, distinct; ovary glabrous and sometimes glandular, on a stipe to 0.3 mm long.
Legumes reddish-brown, straight to slightly curved, flattened, strongly constricted between the seeds, linear, 50-150 x 3.6-5.6 mm, chartaceous, reticulately striate, glabrous and not glutinous, usually eglandular but sometimes with small reddish glands, dehiscent; a chartaceous pericarpic strip lining each valve; stipe to 8 mm long; apex acuminate and usually beaked.  Seeds uniseriate, no pulp, mottled gray-black, oblong, strongly flattened, 5.0-7.1 x 2.5-3.6 mm, smooth; pleurogram oval to U-shaped, 0.5-1.0 mm across. Flowers in April to October. Chromosome number:  2n = 52 (Turner and Fearing 1960)

Distribution

Disturbed, arid sites in diverse soil types, between 600 and 2,000 m elevation from western Texas to southwestern Arizona, south through much of the thorn scrub and desert regions of Mexico to the states of Puebla and Oaxaca (Clarke et al. 1990).

Additional info

Vachellia constricta is relatively consistent in most characteristics, but some variation does exist, particularly in leaf size, pubescence, and stipular spines.  The short shoot leaves generally are small, with few pinnae and smaller leaflets than the primary leaves, that originate between the stipular spines on new growth.  Also, specimens from the southern part of the range sometimes have slightly longer (4.0 mm) and broader (1.5 mm) leaflets.  Typical V. constricta has lightly puberulent petioles, peduncles, and rachises, whereas the leaflets are glabrous and only lightly ciliate.  Many collections from the northern part of the range, in contrast, have densely pubescent petioles, peduncles and rachises, ciliate leaf margins and occasionally pubescent leaflets.  Stipular spine length also is highly variable.  In some specimens, the spines are well developed and up to 35 mm long, in other specimens the spines are reduced to hard stipules, and sometimes are absent.  This character is somewhat variable on individual plants, with some branches lacking spines; at the same time others have well developed spines.  This nearly spineless form appears to be more common in the northern part of the range in Arizona and New Mexico, and has been given varietal status (var. paucispina) (Wooton and Standley 1909).  The variation existing in single individuals as well as within populations suggests that this characteristic represents random variation, and these plants do not require varietal status.  Other characteristics mentioned by the authors do not appear to be correlated with the spineless condition (Isely 1969).

Vachellia constricta is closely related to V. vernicosa (syn. A. neovernicosa), which was originally considered within the concept of V. constricta.  The two species are easily separated, except for a few specimens from areas where the species are sympatric.  In general, V. vernicosa has glutinous leaves, twigs and fruits; is mostly glabrous throughout; and has 1-2 (3) pairs of pinnae; whereas V. constricta lacks glutinous leaves, twigs and fruits, generally is pubescent, and has leaves with up to 8 pairs of pinnae.  Possible hybridization between V. constricta and V.vernicosa has been reported by Clarke et al. (1990).

Most specimens of Vachellia constricta test positive for cyanide.  Clarke et al. (1990) reported that 98% of the specimens tested gave a positive reaction.  More recently, 55 specimens from the southwestern United States were tested, with over 90% giving a positive reaction.  All of the specimens that gave a negative reaction were nearly 100 years old, indicating that the cyanogenic glycoside decomposes on prolonged storage.  Living material of this species tested in the field, consistently gives a strong positive reaction for hydrogen cyanide.  The cyanogenic glycoside responsible is proacacipetalin (Seigler et al. 1976).

Flowering time

April - October.

Representative specimens

UNITED STATES:

Arizona:

Cochise Co.:

Gila Co.:

Graham Co.:

Greenlee Co.:

Maricopa Co.:

Pima Co.:

Pinal Co.:

Yavapai Co.:

Yuma Co.:

New Mexico:

Dona Ana Co.:

Grant Co.:

Hidalgo Co.:

Luna Co.:

Sandoval Co.:

Socorro Co.:

Texas:

Brewster Co.:

Culberson Co.:

El Paso Co.:

Howard Co.:

Hudspeth Co.:

Loving Co.:

Jeff Davis Co.:

Presidio Co.:

Reeves Co.:

Starr Co.:

Terrell Co.:

MEXICO  Baja California Sur:

Chihuahua:

Coahuila:

Durango:

Nuevo León:

Oaxaca:

Puebla:

Querétaro:

San Luis Potosí:

Sonora:

Tamaulipas:

Veracruz:

Zacatecas:

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