Costus dubius (Afzel.) K.Schum., Costaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  High risk, score: 8 (Go to the risk assessment)

Habit:  herb

Description:  Tall perennial herb up to 2 m high.  Leaves numerous, borne on tall stems.  Inflorescences with numerous flowers; leaves obovate-elliptic, cuneate at the base, long-acuminate, 10-31 cm long, 3-7 cm broad, pubescent, shortly petiolate.  Each bract covering one flower; bracts (except sometimes outer ones) not leafy at apex; leaf-sheaths without a rim below the apex.  Flowers white with yellow throat; succulent inflorescences either terminating the leafy shoots or short leafless stems at their foot, ochrea as along as broad; leaves shortly appressed-pubescent (adapted from Hepper, 1968; pp. 77-78).

"The leafy stems reach ca. 2 m in height, with the inflorescences borne on separate stalks arising from the rhizome. The inflorescence is rounded, with tightly fitting green bracts, out of which white flowers with a yellow-centered labellum arise. A single flower is borne in each bract" (Daehler & Baker, 2006; p. 6).

Habitat/ecology:  In the rain forest in its native habitat (Africa) (Hepper, 1968; p. 78).

In Hawai‘i (O‘ahu), "growing wild in Oplismenus grass, Haukulu, Lyon Arboretum", "this plant has become a major problem wherever it was planted" (Daehler & Baker, 2006; p. 6).

Propagation:  "It produces copious quantities of seed" (Daehler & Baker, 2006; p. 6).

Native range:  Africa (Daehler & Baker, 2006; p. 6).

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	Kaua‘i Island		Bishop Museum (U.S.A. Hawaii. Honolulu.) (1997) (voucher ID: BISH 653240) Taxon name on voucher: Costus dubius (Afzel.) K.Schum.
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive cultivated	Daehler, Curtis C./Baker, Raymond F. (2006) (p. 6) Voucher cited: C. Daehler 1060 (BISH, HAW); K. Nagata 2307 (HLA)

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

Information about Costus dubius as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

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

References:

Bishop Museum (U.S.A. Hawaii. Honolulu.). 1997. Voucher specimen #BISH653240(Lorence, D.H. 7949).

Daehler, Curtis C./Baker, Raymond F. 2006. New records of naturalized and naturalizing plants around Lyon Arboretum, Mānoa Valley, O‘ahu. In: Evenhuis, Neal L. and Eldredge, Lucias G., eds. Records of the Hawaii Biological Survey for 2004-2005. Part 1: Articles. Bishop Museum Occasional Papers 87:3-18.

Hutchinson, J./Dalziel, M. D./Keay, R. W. J. 1954. Flora of West Tropical Africa, second edition. Crown Agents, London.