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Vachellia aroma var. aroma - spines

Vachellia aroma var. aroma - habit

Vachellia aroma var. aroma - leaves

Vachellia aroma var. aroma - pods

Vachellia aroma var. aroma - pods

Name

Vachellia aroma (Gillies ex Hooker & Arnott) Seigler & Ebinger, Phytologia 87:143. 2005.
syn. Acacia aroma Gillies ex Hook. & Arn. Bot. Misc. 3:206. 1833.

Synonymy and types

Basionym:  Acacia aroma Gillies ex Hook. & Arn. Bot. Misc. 3:206. 1833. - Acacia lutea (Mill.) Britton var. aroma (Gillies ex Hook. & Arn.) Kuntze, Revis. gen. pl. 3(2):47. 1898. - Vachellia lutea (Mill.) Speg. var. aroma (Gillies ex Hook. & Arn.) Speg., Bol. Acad. Nac. Ci. Córdoba 26:307. 1924. - Vachellia lutea (Mill.) Speg. f. aroma (Gillies ex Hook. & Arn.) Speg., Bol. Acad. Nac. Ci. Córdoba 26:313. 1924. - TYPE: ARGENTINA. a little way south of San Juan, Dec. 1823, J.Gillies s.n. (holotype: K).

Acacia moniliformis Griseb., Abh. Königl. Ges. Wiss. Göttingen 19:136. 1874. - Acacia lutea (Mill.) Britton var. moniliformis (Griseb.) Kuntze, Rev. gen. pl. 3(2):47. 1898 (as monoliformis). - Vachellia lutea (Mill.) Speg. var. moniliformis (Griseb.) Speg., Bol. Acad. Nac. Ci. Córdoba 26:303. 1924. - Vachellia lutea (Mill.) Speg. f. moniliformis (Griseb.) Speg., Bol. Acad. Nac. Ci. Córdoba 26:312. 1924. - TYPE: ARGENTINA. TUCUMAN: La Cruz, 20-24 Apr. 1872, T.G.Lorentz 190 (holotype: GOET).

Acacia michelii Rusby, Mem. Torrey Bot. Club 6:28. 1896. - TYPE: BOLIVIA. vic Cochabamba, 1891, M.Bang 1095 (holotype: K; isotype: NY).

Acacia aroma Gillies ex Hook. & Arn. var. cochlearis Griseb., Abh. Königl. Ges. Wiss. Göttingen 24:122. 1879. - TYPE: ARGENTINA. CÓRDOBA: north of San Javier, 18 Mar. 1876, T.G.Hieronymus 558 (holotype: GOET).

Vachellia lutea (Mill.) Speg. f. oocephala Speg., Bol. Acad. Nac. Ci. Córdoba 26:312. 1924. - TYPE: none cited.

Vachellia lutea (Mill.) Speg. f. thlipsacantha Speg., Bol. Acad. Nac. Ci. Córdoba 26:312. 1924. - TYPE: none cited.

Vachellia lutea (Mill.) Speg. var. aroma (Gillies ex Hook. & Arn.) Speg. f. leptocarpa Speg., Bol. Acad. Nac. Ci. Córdoba 26:305. 1924. - TYPE: none cited.

Vachellia lutea (Mill.) Speg. var. aroma (Gillies ex Hook. & Arn.) Speg. f. pachycarpa Speg., Bol. Acad. Nac. Ci. Córdoba 26:307. 1924. - TYPE: none cited.

Formal description

Large shrub to small tree 6 m tall. Bark dark gray to dark brown, smooth to shallowly furrowed. Twigs light to dark purplish brown, slightly flexuous, glabrous to densely puberulent. Short shoots sometimes present above the stipular spines particularly on slow growing branches, to 2 mm long, covered with acuminate stipules and old leaf bases, sometimes developing into long shoots. Leaves alternate, also occasionally clustered on the short shoots, 60-140 mm long. Stipular spines reddish brown, usually becoming light gray with age, symmetrical, terete to angular or rarely flattened, straight, stout, to 10(60)mm x 1.0-2.5 mm near the base, glabrous to puberulent at the base and sometimes throughout. Petiole adaxially grooved, 5-9 mm long, glabrous to lightly puberulent; petiolar gland solitary, located medially to just below the first pinna pair, sessile, circular to elongated, 0.7-1.8 mm long, apex usually depressed to rarely bulbous, sometimes puberulent. Rachis adaxially grooved, 30-135 mm long, usually lightly puberulent, a sessile, circular gland, 0.2-0.6 mm across, between the upper 1 to 3 pinna pairs. Pinnae (4)12 to 29 pairs per leaf, 18-31 mm long, 2.5-6.0 mm between pinna pairs. Petiolules 0.4-1.1 mm long. Leaflets 24 to 50(58) pairs per pinna, opposite, 0.4-0.9 mm between leaflets, linear, 1.5-4.1 x 0.5-0.8 mm, glabrous to lightly puberulent, lateral veins not obvious, only one vein from the base, base oblique, margins lightly ciliate, apex broadly acute to obtuse. Inflorescence a densely flowered globose head, 7-10 mm across, solitary (rarely 3) from the nodes. Peduncles 22-40 x 0.4-0.7 mm, usually lightly puberulent. Involucre 4- to 6-lobed, located at the base of the globose head, puberulent, persistent. Floral bracts spatulate, 1.3-1.9 mm long, apex puberulent, deciduous. Flowers sessile, pale yellow; calyx 5-lobed, 1.3-1.8 mm long, the lobes densely puberulent; corolla 5-lobed, 2.0-2.7 mm long, the lobes commonly puberulent; stamen filaments 2.5-4.0 mm long, distinct; ovary glabrous to lightly pubescent, on a stipe to 0.2 mm long. Legumes dark reddish brown, straight to slightly curved, flattened to elliptical in cross section, constricted between the seeds, oblong, 30-150 x 9-15 mm, coriaceous, reticulately striate, usually densely puberulent, eglandular, indehiscent; stipe to 6 mm long; apex acute, narrowing to a beak to 15 mm long. Seeds uniseriate, no pulp, light to dark brown, ovoid to nearly circular, strongly flattened, 5.3-7.3 x 4.0-6.2 mm, smooth; pleurogram nearly oval, 2.5-4.0 mm across. Flowers from September to February. Chromosome number: Not determined.

Distribution

Shrubby vegetation of pastures, successional field, edge of roads, sandy floodplains and other disturbed sites, thorn -scrub forests, and chaco scrub forest from near sea level to 3000 m in central and northern Argentina, Bolivia, western Paraguay and north to Peru and Ecuador.

Additional info

Vachellia aroma var. aroma is a wide-ranging species extending through most of the drier regions of southern South America. It is common in many areas where V. caven occurs, particularly in northern Argentina, Bolivia and Paraguay. Vachellia aroma is an invasive species, with many of the collections from pastures, successional fields, and roadsides.  Like V. caven, this taxon seems to be characterized by a great deal of ecological variation.  It occurs from near sea level to 3000 m, probably being limited by freezing temperatures.  It also occurs from extremely dry Larrea associations to thorn scrub and dry forests to stream banks.

The only species in South America that Vachellia aroma var. aroma is usually confused with is V. macracantha. Both species have relatively large leaves with mostly more than 11 pinnae pairs, a characteristic limited to these two taxa and V. pennatula. Though superficially similar, numerous characteristics can be used for consistent separation. Vachellia aroma has flattened fruits that are constricted between the seeds; many of the peduncles are more than 25 mm long; the petiole glands are sessile; and the petiole, and rachis are puberulent with short, erect hairs that are less than 0.2 mm long. Vachellia macracantha, in contrast, has flattened fruits that are not constricted between the seeds, the peduncles are less than 25 mm long, the petiole gland is stalked, and the pubescence, if present, is of erect hairs that are more than 0.3 mm long.

Besides the characteristics listed above, short shoots are sometimes found in Vachellia aroma, while they are mostly absent in V. macracantha. These short shoots occur on slow growing branches were they develop just above the stipular spines in the axil of primary leaves. The primary leaves commonly have 12 to 29 pinnae pairs with relatively large leaflets. The leaves that develop from the short shoot are generally smaller, commonly with 4-15 pinnae pairs and leaflets than are less than 2.3 mm long. It is not uncommon for these short shoot leaves to lack a petiole gland, or the gland is smaller and more bulbous than on the larger leaves.

Throughout its extensive geographic range and habitats in which Vachellia aroma var. aroma occurs, this taxon is highly variable in some morphological characteristics.  Extensive variation occurs in leaf size and pubescence, as well as in the overall size of the plants. Most of the specimens observed from east of the Andes Mountains, the vegetative parts of the plants were usually glabrous to lightly puberulent, particularly the petioles, rachises, petiolar glands and leaflets; while the primary leaves were longer, with more and longer pinna that had more leaflet pairs. Specimens from west of the Andes Mountains usually had densely puberulent petioles, rachises, leaflets and petiolar glands; while the primary leaves were smaller with fewer and shorter pinna that had fewer pairs of leaflets. Also, the information on the herbarium labels indicated that the specimens east of the mountains were on the average larger and more robust than those from west of the mountains.

It appears that Vachellia aroma var. aroma is only rarely cyanogenic. Aronson and Nash (1989) reported negative results for this species, while Aronson (1990) found some seedlings to be slightly to moderately cyanogenic. Of the 220 specimens test during the present study 215 gave a negative reaction even after the addition of emulsin. A weak positive cyanogenic reactions was observed in five specimens.  Seigler and Conn (1982) found linamarin and lotaustralin to be the principal glycosides in this species.

The two varieties of Vachellia aroma (aroma and huarango) are easily separated since var. aroma is a large shrub or small trees with an wide distribution throughout much of southern South America. Variety huarango, in contrast, is a low dense shrub usually less than 1.5 m tall, and is commonly broader than tall with a restricted distribution, occurring in Ecuador and Peru.

Flowering time

September-February.

Representative specimens

ARGENTINA:

Catamarca:

Chaco:

Córdoba:

Corrientes:

Formosa:

Jujuy:

La Rioja:

Salta:

San Juan:

San Luis:

Santa Fe:

Santiago del Estero:

Tucumán:

BOLIVIA:

Cochabamba:

Chuquisaca:

La Paz:

Potosí:

Santa Cruz:

Tarija:

State not known:

ECUADOR:

Guayas:

PARAGUAY:

Boquerón:

Central:

Chaco:

Nueva Asunción:

Presidente Hayes:

PERU:

Amazonas:

Ancash:

Apurímac:

Ayacucho:

Cajamarca:

Cuzco:

Huánuco:

La Libertad:

Lambayeque:

Paita:

Tumbes:

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