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PLANT FAMILY: Costaceae
BOTANICAL NAME: Costus dubius
FORMAL SCIENTIFIC NAME: Costus dubius (Afzel.) K.Schum.
SYNONYMS: Costus albus, Costus edulis, Costus trachyphyllus,
This African species is recognized in Paul Maas' monograph on African Costaceae, published on 16 December 2016. (Monograph of African Costaceae, H. Maas-van de Kamer, P.J.M. Maas, J.J. Wieringa, C.D. Specht, Blumea 61, 2016: 280 - 318, http://www.ingentaconnect.com/content/nhn/blumea/2016/00000061/00000003/art00010)
The African Plant Database lists this as an accepted species.
There are several African species that are easily confused with each other as they are superficially similar looking. The various names and PIDs where information is stored on this website are as follows:
Costus afer -PID 3430 - 2 flowers per bract
Costus albus -PID 4868 - single flower per bract
Costus dallachyi - on tag at National Tropical Botanic Garden
Costus deistelii -PID 3754
Costus dinklagei -PID 7279
Costus dubius -PID3597 - single flower per bract
Costus maculatus -PID 3604 -2 flowers per bract
Costus megalobractea -PID 3755
These plants have also been circulated from Europeon botanical gardens originating at the Severoceska Bot. Garden in Czech Republic under the name Tapeinochilos spectabile - believed to actually be Costus maculatus.TAXONOMY NOTES BY BRIAN MIDDLEDITCH - Costus dubius (Afzel.) Schumann: Adam Afzelius named the species Zingiber dubium in 1813 (I don't know why). It was reclassified as Costus dubius in 1904 by Schumann.
Schumann describes this species and places in subgenus Eucostus - Das Pflanzenreich IV, 1904.
National Botanic Garden of Belgium (from Democratic Republic of Congo )
W3Tropicos - http://mobot.mobot.org/W3T/Search/pick.html - CAMEROON = Specimen data: Herb 2 m high. Inflorescence from base of leafy shoot. Flower white with yellow center. TANZANIA = Specimen data: Herb ca. 1 m tall, somewhat succulent. Inflorescence borne separately from flowering stem; petals white, fleshy; one large petal tinged yellow inside; anthers white; pistil white. Common near river bank. Local name: "Jamii ya masegenya" (Kiha).
Tested for winter hardiness by Tom Wood near Gainesville, Florida - zone 8b-9, did not survive.
GINGERSRUS CATALOG LISTING:
I have seen this Costus in many botanical gardens and conservatories, but have not seen it for sale in the horticultural trade. It comes from Africa, another of the dozen or so lessor-known species of Costus in cultivation that come from the tropical areas of that continent. Costus dubius is a basal bloomer which produces white flowers with yellow centers on the labellum, protruding from a tight ball of green bracts. The flower is similar looking to Costus maculatus, except that it produces a single flower per bract whereas C. maculatus produces two flowers per bract. Costus dubius makes up for this by producing many more inflorescenses in a tighter area, almost forming a carpet of flowers in some cases.
Hardiness has not been fully tested, but based on it's relative ease of cultivation and survival in a cool greenhouse, I am guessing hardiness as zone 9 and that it would come back okay from occasional light freezes. This seems to be a sun loving Costus species, and I recommend growing it in partial sun. As with other Costus species, regular moisture during active growth and fertile organic soil.