Costus spectabilis

Auxiliary rosette of leaves attempting to emerge but crowded out by main rosette.

 

Yesterday our Costus spectabilis bloomed for the first time. What an exciting event! The flower is ephemeral lasting only one day, but the plant is a sequential bloomer.

 

Most gingers and other zingiberales technically meet the criteria for what constitutes a geophyte, but this species is rather unique for its genus and fits even the most stringent qualifications for this category. It goes completely dormant during the dry winter, retreating back to a centipede-like rhizome that lacks perennial roots. Unlike other Costus, this acaulescent species doesn't form aboveground stems. After a dry winter rest, the combination of warmth and water in late spring cause it to pierce through the bare ground, opening beautiful rosettes of round paddle leaves that will appress themselves to the soil once fully formed. The plants are somewhat reminiscent of Massonia or lily pads floating on the surface of the earth. New leaves have an attractive golden sheen, and many clones have gorgeous red ciliate leaf margins. The abaxial leaf surface consists of a spongy white texture, akin to styrofoam.

 

The flowers are brilliant yellow, sort of resembling a squash blossom, 9cm wide. When it fades, it also resembles a squash blossom! The petals are not very conspicuous, however the real showy part of the flower is the large staminodial labellum. The texture is so soft and thin, with a crisped margin. Perhaps the most delightful floral detail is that it sparkles in sunlight! This rhizomatous geophyte is native to much of tropical Africa: Benin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Mali, Nigeria, Senegal, Sierra Leone, Togo, Burundi, Cameroon, Gabon, DRC, Chad, Ethiopia, Sudan, Kenya, Tanzania, Uganda, Angola, Malawi, Zambia, and Zimbabwe. Surprisingly it is rare in cultivation, at least outside of the African continent.

 

When grown in a pot, as shown in my pictures, the curious centipede-shaped rhizomes circle the pot causing the rosettes of leaves to grow crowded together instead of spreading out. Last year I grew it outdoors in Upper Mānoa Valley, a wet montane tropical environment. It grew well but did not bloom. I suspect that this was due to a lack of strong sunlight and heat (other heat-loving geophytes also failed to bloom in this situation i.e. Bessera elegans, Milla magnifica). This year I placed it under a sodium halide light in my indoor orchid vivarium. It received high light (5500fc), 14-hour days, high humidity, air movement, daytime temp 27°C, night-time temp 20°C. I moved it out to enjoy the bloom and in the past few days the leaves have surprisingly raised themselves into a more diagonal orientation. I think this may be a response to lower light intensity.

 

This is a promising horticultural subject for climates with warm humid summers. Certainly this would be a wonderful garden plant in seasonally dry tropical lowlands such as leeward/Kona Hawai'i, extreme S Florida, much of S and SE Asia, Queensland, India, Caribbean, Meso- and S America and Africa. It is not hardy outdoors in S California. It should be kept dry in dormancy, so folks in climates with non-tropical winters can simply bring the pots indoors and keep them dry on a shelf or in a box until the following spring. Shallow wide bulb pans are best. I suspect this would grow well as a potted tender perennial in the US South and East Coast.

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Taken on May 26, 2010