Present on Pacific Islands?  yes

Threat only at high elevations?  no

Common name(s): [more details]

Hawaiian: oī, ōwī

Habit:  herb

Description:  "Annual or perennial herbs up to 20 dm tall, becoming somewhat woody toward base; stems dichotomously branched, younger stems moderately to densely short-pubescent.  Leaves opposite, membranous or chartaceous, elliptic to ovate or narrowly ovate, 1.5-10 cm long, 1-5 cm wide, upper surface puberulent to strigillose or scaberulous, lower surface sparsely to moderately strigillose over entire surface, margins serrate to crenate-serrate, the teeth angled forward, apex sharply acute to acuminate, petioles 0.3-1 cm long.  Spikes slender, 15-45 cm long, up to ca. 3 mm in diameter, somewhat flaccid, usually short-pubescent throughout, the furrows nearly as wide as the rachis, bracts narrowly lanceolate, ca. 5 mm long; calyx ca. 6 mm long, the teeth subequal; corolla pale blue to blue, pale violet, or lavender, occasionally white"  (Wagner et al., 1999; pp. 1321-1322).

"This species is reported to hybridize with Stachytarpheta jamaicensis" (Wagner et al., 1999; pp. 1321-1322).

Keys to the species (Smith, 2002; pp. 42-43):

S. australis:  Lower leaf surfaces, rachis and calyx hairy; flowers pale blue or almost white.
S. cayennensis:  Lower leaf surfaces, rachis and calyx hairless; rachis slender 1-3 mm diameter; leaves membranous; flowers blue to almost white.
S. jamaicensis:  Lower leaf surface, rachis and calyx hairless; rachis stout, 3-5 mm diameter; leaves fleshy; flowers mauve, blue, violet or purple.

Habitat/ecology:  "Snakeweeds invade disturbed areas, e.g. creek lines and roadsides; also monsoon vine forests where soil has been disturbed by pigs and buffalo. Can invade overgrazed pastures." (Smith, 2002; pp. 42-43). In Hawai‘i, "naturalized in usually mesic, disturbed sites, 170-1,340 m" (Wagner et al., 1999; pp. 1321-1322).

Propagation:  "Usually spread intentionally as ornamental plants.  Seeds are also dispersed on vehicles, by the movement of soil in refuse from gardens and by rainwater.  In Queensland [Australia] they have been spread in fodder, hay and in contaminated pasture seed."  (Smith, 2002; pp. 42-43).

Native range:  "Apparently native from Cuba and Mexico south to Peru and Argentina, now widely naturalized in tropical and subtropical areas" (Wagner et al., 1999; pp. 1321-1322).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 1322-1323, 1896)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 1322-1323, 1896)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 1322-1323, 1896)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 1322-1323, 1896)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 1322-1323, 1896)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	Northern Territory	introduced invasive cultivated	Smith, Nicholas M. (2002) (pp. 42-43)
Australia Australia (continental)	Queensland	introduced invasive cultivated	Smith, Nicholas M. (2002) (pp. 42-43)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 351)

Comments:  A declared noxious weed in Western Australia (Smith, 2002; pp. 42-43).

Additional information:  Additional online information about Stachytarpheta australis is available from the Hawaiian Ecosystems at Risk project (HEAR).

Taxonomic information about Stachytarpheta australis may be available from the Germplasm Resources Information Network (GRIN).

References:

Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. 1979. A geographical atlas of world weeds. John Wiley & Sons, New York. 391 pp.

Smith, Nicholas M. 2002. Weeds of the wet/dry tropics of Australia - a field guide. Environment Centre NT, Inc. 112 pp.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).