Flora of the Hawaiian Islands
Dicotyledon Literature for Stachytarpheta cayennensis
Lorence & Wagner, 2020.
   Verbenaceae -- The Verbena Family Bibliography
      Stachytarpheta cayennensis

Common name(s): oi, owi
General Information
DistributionNative to South and Central America and the Caribbean, now widely naturalized in tropical and subtropical areas.In the Hawaiian Islands, naturalized on Kaua`i, O`ahu, Moloka`i, Maui, Hawai`i.

Coarse, perennial herb, 0.8‒2 m tall, sometimes somewhat woody toward base; stems usually weakly erect, intricately branched, very sparsely puberulent.
Leaves opposite, short-petiolate; blade membranous, elliptic to broadly elliptic or ovate, 4‒8 cm long, 2‒4.5 cm wide, adaxial surface rugose, both surfaces glabrous or occasionally abaxial surface with very few scattered hairs usually along the veins and margin, margin sharply and coarsely serrate, teeth conspicuously divergent, secondary veins 5‒7 on each side, apex acute, base cuneate; petiole 0.5‒2 cm long, winged above.
Inflorescences a slender spike, rachis flexuous to erect or somewhat nodding, 14‒40 cm long, ca. 2.5 mm in diameter, furrows somewhat shallow, nearly as wide as the rachis; bracts lanceolate, 4.5‒7 mm long, 1‒1.2 mm wide. Flowers with calyx ca. 7 mm long, teeth subequal; corolla usually dark purplish blue with a paler center, tube 7‒8 mm long.
Fruit oblong-ovoid, compressed, bicarinate, 5‒6 mm long, 1.5‒1.7 mm wide.
Seed ellipsoid-compressed, 3‒3.5 mm long, 1‒1.2 mm wide, black, beaked with persistent style base.
David Lorence