2 Costus dubius

Costus dubius.

Naturalised in N. E. Queensland they are used as garden or house plants.
They are herbaceous or woody perennial plants up to 5 or 6 m high.
Stems, from underground rhizomes form small clumps.

The lower part of the stem is bare with spirally arranged elliptic to obovate leaves above.
On petioles around 5 mm long the blades are 20 to 30 cm long.
The petiole continues down the stem as a sheath with closed edges.

Each inflorescence is on a stalk around 30 to 40 cm high.
Apart from a whorl of 4 leaves immediately under the inflorescence the stems are bare.
The cone-shaped spike has overlapping green spirally arranged bracts with a blunt tip.
Each fleshy bract holds 1 narrow funnel-shaped flower.

The 3 petals are white and the larger labellum is white with a yellowish centre.
The labellum has an irregularly toothed margin.

The single petal-like fertile stamen filament extends just past the perianth.
It holds the 2 pollen sacs of the anther.
The style runs between the anther sacs with the large stigma held just above the sacs.