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Acacia millefolia

Family: Fabaceae

Description: This species of Acacia differs from others by the following combination of characteristics: leaves bipinnate, flowers in spikes, plants unarmed or only slightly thorny, the pinnae in (4)6-10 pairs.

Distribution: Isely (1973) records this species from Arizona and Mexico; Kearney and Peebles limit this general range slightly by stating that the species occurs in southern Arizona and northern Mexico. Wiggins (1964) indicate the species to be from Arizona, Sonora and Chihuahua. Britton and Rose (1928) give the type locality of this species [Senegalia millifolia (S. Wats.) Britt. & Rose] as the Hacienda San Jose in Chihuahua. This may be at the present San José de Babícora in western Chihuahua about 300 km south of the Mexico-US border for this was an important early collecting area, but without access to early literature and knowledge of the collector's itinerary the site must remain indefinite for the time being. Spellenberg et al. (1986) report the species for the first time in extreme southwestern New Mexico a few meters north of the Mexico-US border.

Plants Seen or Cited: New Mexico, Hidalgo Co.: Guadalupe Canyon and tributaries in extreme SW corner of county, on & in vicinity of Hadley Ranch, ca. 50 m N of Mexican border, ca. 1/2 mi E of Arizona, W edge S24, T24S, R22W, 17 Aug 1979, Spellenberg & Repass 5371 (NMC). There are two sheets of this species from Arizona at UTEP.

Habitat: Ledges, desert grassland, open rocky slopes, foothills, 4,000-5,000 ft. (Isely 1973); generally igneous rock with sparse oak, juniper, and Mexican pinyon on rocky hills (Spellenberg & Repass 5371).

Discussion: Martin and Hutchins (1980) do not indicate that this species might be expected in New Mexico. Isely (1973) notes this species to be "locally abundant," his treatment exclusively north of the Mexico-US border (thus he means in Arizona). In contrast, Kearney and Peebles (1969) say that the species is "apparently rare.". The following do not record the species in their areas of concern: Estrada C. et al. (1997) - Babícora region, Chihuahua; González E. et al. (1991) - Durango; Henrickson and Johnston (1997) - Chihuahua Desert region; Martin, Jenkens et al. (1990) - Río Mayo region of Chihuahua and Sonora; Spellenberg et al. (1996) - Basaseachi, Chihuahua. Thus, with information available at this time, the extent of the range of the species can be ascertained only to be restricted to the four states, Arizona, Sonora, Chihuahua, and New Mexico, most likely in the lower Madrean vegetation region in the northern Sierra Madre Occidental, but the extent of the distribution cannot be determined except to suggest that it does not extend as far south as central Chihuahua and adjacent Sonora. This is apparently a regional endemic in the northern Sierra Madrean area, apparently rare but locally common in southeastern Arizona and extending into New Mexico in the southwestern corner of the state by a very small distance.

Important Literature:

Britton, N.L, and J.N. Rose. 1928. Mimosaceae (continuatio). North American Flora 23(2): 77-136.

Estrada C., A.E., R. Spellenberg, and T. Lebgue. 1997. Flora vascular de la Laguna de Babícora, Chihuahua, México. Sida 17(4): 809-828.

González E., M.S. González E., Y. Herrera A. 1991. Flora de Durango. Listados Florísticos de México, IX. Instituto de Biología, Universidad Nacional Autónoma de México, México. 167 pp.

Isely, D. 1973. Leguminosae of the United States: I. Subfamily Mimosoideae. Mem. N. Y. Botanical Gard. 25(1): 1-150.

Kearney, T.H. and R.H. Peebles. 1969. Arizona Flora, 2nd ed. (with supplement by J.T. Howell, Elizabeth McClintock, et al.). Univ. California Press, Berkeley. 1085 pp.

Martin, P.C., P. Jenkins, and others. 1990. Manuscript checklist of the plants of the Rio Mayo region in western Chihuahua and southern Sonora. 351 mss pages (no authors indicated).

Spellenberg, R., T. Lebgue, and R. Corral-Díaz. 1996. A specimen-based, annotated checklist of the vascular plants of Parque Nacional "Cascada de Basaseachi" and adjacent areas, Chihuahua, México. Listados Florísticos de México, XIII. Instituto de Biología, Universidad Nacional Autónoma de México, México. 72 pp.

Spellenberg, R., R. Worthington, P. Knight, & R. Fletcher. 1986. Additions to the flora of New Mexico. Sida 11(4):455-470.

Wiggins, I.L. 1964. Flora of the Sonoran Desert. Part II; pp. 189-1699 in: F. Shreve and I.L. Wiggins, Vegetation and Flora of the Sonoran Desert. Stanford Univ. Press, Standford. 2 vols, 1740 pp.

Information Compiled By: Richard Spellenberg 1998

Photo credits in header Peniocereus greggii var. greggii © T. Todsen,
Lepidospartum burgessii © M. Howard, Argemone pleiacantha ssp. pinnatisecta © R. Sivinski
Design: J. Mygatt; Copyright © 1999-2005 New Mexico Rare Plant Technical Council