Flowers of Costus woodsonii or Scarlet Spiral Flag

The two recent posts of Costus spicatus (Indian Head Ginger) showing an interesting feeding behaviour of the Brown-throated Sunbird (Anthreptes malacensis) led me to take a closer look at the plant and its flowering biology LINK 1 and LINK 2.

As a result of the above, it was found that the plant had been mis-identified in the above two posts and possibly others as well. The proper name of this common ginger plant should be Costus woodsonii (Scarlet Spiral Flag) (above). And according to Whistler (2000), such mis-identification is quite common.

This Scarlet Spiral Flag, commonly known in the ornamental plant trade as French Kiss, originates from Panama and Costa Rica. It is now widely grown in the tropics for its attractive bright red, ovoid to cylindrical flowering head which is made up of closely packed bracts. The yellow to orange flowers appear singly at intervals of a few days, starting from the lowermost bract and moving up to the top.

The flowers attract Brown-throated Sunbirds that need to pry open the tubular petals to get at the nectar inside. In its native country these flowers are pollinated by hummingbirds. So this local sunbird has obviously learnt how to exploit the nectar from this exotic plant. I can only conclude that the distance from the top of the flower to its base is more than the length of the sunbird’s tongue.

However, this may not be the case with other species of sunbirds. Check out the image in this LINK where the Olive-backed Sunbird (Cinnyris jugularis) appears to be stealing nectar by probing the base of the flower. Or this LINK, where the female Brown-throated Sunbird (or can it be a different species?) taking nectar from the top opening of the flower.

The flowers of this popular ginger plant slip out of the tightly overlapping bracts in the early morning (top). They only last a day. The above image (left) shows the flower the next morning as it is about to droop. The image on the right shows the empty space between the flowering bract and the flowering head after flower has dropped off.

The three orange sepals enclose the three petals that are fused half way up. The flowers do not unfold as with most other flowers. There is only a small opening at the top where the sepals and petals separate out very slightly. Thus the necessity to pry the petals open. The image on the left shows the long-section of a flower and its various parts.

From morning till late evening, a continuous stream of small ants (about 2mm long) moved in and out of this small opening at the top of the flower (above). These ants, coming from the ground below, were obviously collecting nectar. Once in a while some ants can be seen with masses of white pollen between their mandibles (below). By dusk the ants stopped visiting and by the next morning the flower got detached from the flowering head.

Through the courtesy of Wang Luan Keng of The Nature Workshop, Singapore LINK, we managed to get Eunice JY Soh, a 4th year National University of Singapore biology undergraduate to identify the ants LINK. It is to be noted that these tiny ants need close microscopic examination before a proper identification can be made. However, provided with only a few images that failed to show the crucial morphological parts for proper identification, Eunice managed to put a name to these ants. According to her, the ants are probably Monomorium floricola.

Photographers and videographers are urged to make documentations of nectar harvesting by sunbirds and other nectivorous birds on this Costus species – to possibly discover more interesting feeding behaviour.

YC Wee, Eunice JY Soh & Wang Luan Keng
Singapore
January 2014

Reference:
Whistler, W. A. (2000). Tropical Ornamentals – a guide. Timber Press, Portland, Oregon.