Costus spectabilis: 'Massonia' of tropical Africa

Jacob Knecht
Fri, 28 May 2010 20:25:28 PDT
Dear Members,

Two days ago 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 Pacific Bulb
Society 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 (O'ahu, Hawai'i), 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

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.

Selected pictures of our plant:………………
In situ* pictures:……


Jacob Uluwehi Knecht


More information about the pbs mailing list