Name
Vachellia janzenii (Ebinger & Seigler) Seigler & Ebinger, Phytologia 87: 160. 2005. syn. Acacia janzenii Ebinger & Seigler, Southw. Naturalist 32: 245. 1987.
Synonymy and types
Basionym: Acacia janzenii Ebinger & Seigler, Southw. Naturalist 32: 245. 1987. - TYPE: MEXICO. TABASCO: 9.8 miles W of Lázaro Cárdenas on hwy. 180, 17 Jun 1966, D. H. Janzen 515 (holotype: MO; isotypes: BM, CAS, F, GH, MICH, MO, UC, US).
Formal description
Tree to 12 m tall. Bark not seen. Twigs dark reddish brown, not flexuous, lightly puberulent. Short shoots absent. Leaves alternate, 150-370 mm long. Stipular spines dark brown to black, asymmetrical, terete, usually curved around the stem, stout and inflated, 30-60(80) x 6-9 mm near the base, densely pubescent with straight, yellowish hairs to 0.5 mm long. Petiole adaxially grooved, 5-8 mm long, densely pubescent; petiolar glands absent. Rachis adaxially grooved, 140-360 mm long, densely pubescent with yellowish hairs, a sessile, columnar to narrowly volcano-shaped gland located between each pinna pair. Pinnae 30 to 60 pairs per leaf, 40-70 mm long, 6-9 mm between pinna pairs. Petiolules 0.6-1.1 mm long. Leaflets 40 to 70 pairs per pinna, opposite, 0.3-0.8 mm between leaflets, linear, 3-5.5 x 0.6-0.9 mm, glabrous, lateral veins not obvious, only one vein from the base, base oblique, margins ciliate, apex acute; beltian bodies less than 0.7 mm long. Inflorescence a densely flowered globose head, 4-6 mm across, in clusters of 16 to 42 in the axil of slightly reduced leaves on normal branches, also located on fertile branchlets to 250 mm long with 16 to 42 inflorescences in each of 6 to 12 fascicles that may not be subtended by leaves. Peduncles 7-16 x 0.3-0.7 mm, glabrous to lightly puberulent. Involucre usually 4-lobed, located near the middle of the peduncle, glabrous to lightly puberulent, persistent. Floral bracts peltate, 0.4-0.7 mm long, apex circular and ciliate, deciduous. Flowers sessile, pale yellow; calyx 5-lobed, 0.6-1.1 mm long, glabrous; corolla 5-lobed, 1.2-2.1 mm long, about twice as long as the calyx, glabrous; stamen filaments 1.8-2.5 mm long, distinct; ovary glabrous, sessile. Legumes not seen, but probably very similar to those of Vachellia cookii. Seeds not seen. Flowers in May to July. Chromosome number: Not determined.
Distribution
Disturbed sites in open, deciduous forests, roadsides, pastures, and moist disturbed forests, to 400 m elevation, in Chiapas, Tabasco, and Veracruz, Mexico (Ebinger and Seigler 1987, Seigler and Ebinger 1995).
Additional info
Vachellia janzenii is easily distinguished from all other ant-acacias by its asymmetrical stipular spines, which usually curve around the stem and are covered with straight, yellowish hairs to 0.5 mm long. The only other species that consistently has asymmetrical spines is V. cookii. These two closely-related species differ in the petiolar and rachis glands, the type of pubescence on the spines, the leaflet length and width, and the flowering branchlets (Ebinger and Seigler 1987) (see discussion under V. cookii).
Although Janzen (1974) considered this taxon a part of Vachellia cookii, he recognized that the material from southern Mexico (herein referred to V. janzenii) differed from the specimens from farther south in Belize, Guatemala, and Honduras (typical V. cookii). Although he suggested that the extremes were clinally connected, studies by Seigler and Ebinger (1995) suggest that these two species are specifically distinct. No intermediate plants have been found, and the characters used for separation are as significant as those characters used to distinguish other taxa of acacias (Ebinger and Seigler 1987).
Originally, Vachellia janzenii probably was a species of disturbed sites in open forests, particularly landslide scars and stream banks. Most recent collections seen are from roadsides and pastures. Beltian body production in this species is relatively low, usually less than 1/4 of the leaflets contain these bodies. None of the specimens tested positive for cyanide production (Seigler and Ebinger 1995).
Flowering time
May-July.
Representative specimens
MEXICO:
Chiapas:
- stream bank, lower montane rainforest ridge above Ixtacomitan, alt. 300 m, 10 May 1973, D.E.Breedlove 35053 (MEX, MICH, MO);
- 9.8 miles N of turn-off to Tapilula on hwy. from Villa Hermosa to Tuxtla Gutiérrez, 10 Jul 1966, D.H.Janzen 530 (F,MO, NY, UC);
- 10.8 miles S of Pichucalco on hwy. from Villa Hermosa to Tuxtla Gutiérrez, 10 Jul 1966, D.H.Janzen 537 (F, US);
Tabasco:
- 9.8 miles W of Cárdenas on hwy. 180, 17 Jun 1966, D.H.Janzen 515 (F, GH, MEX, MO, UC, US, WIS);
- N margin of Chontalapa, 26 miles S of Cárdenas on road to Presa Malpasa, 17 Jun 1966, D.H.Janzen 548 (F);
- N margin of Chontalapa, 26 miles S of Cárdenas on road to Presa Malpasa, 17 Jun 1966, D.H.Janzen 550 (F);
Veracruz:
- Las Cruces, alt. 250 m, 15 Jul 1970, Nevling & Gómez-Pompa 1555 (F).