The Porcupine Costus

About 10 days ago, a large yellow flower caught my eye on my morning walk. I’ve watched it every day, morning and evening, since, and I’m still amazed that this is a Central American indigenous plant – not something escaped from cultivation.

It was identified as a Costus species by a couple of good folks at Flickr. Being nutty about words, I started by tracking down the word Costus and found, in Dave’s Botanary, that is derived from the Sanskrit name Kushtha. Okay, so then I had to find out what Kushtha was. Turns out it’s a medicinal plant in a group of plants completely unrelated to the Costus group of plants. So, that’s peculiar and of no real help to me. Someday maybe I’ll find out why these flowers were named after other, unrelated plants.

I was, though, able to find out more about the Costus group, and in so doing, ran across David Skinner’s site, GingersRus. It turns out that Costus are closely related to gingers, sometimes being grouped in the same family with them. The Costus group are often called spiral gingers because their leaves spiral up the stem. The spiral is not terribly obvious in the image below, but it’s there, and accounts for asymmetric look of the leaves along the stem.

Back in 1922, when W. W. Rowlee described Costus in Central America (Bulletin of the Torrey Botanical Club) he said, “In any given locality the species do not usually appear abundant, but are scattered about in deep woodlands and undisturbed jungle.” Here’s this plant, in this woodland (although not deep within it), and it’s the only one I’ve seen along my walk, which is about a kilometer long.

Notice the long, thick stems. These are true stems, not the pseudostems (a pseudostem is formed from sheaths at the bases of the stems, like grass) that members of the ginger family, Zingiberaceae, have. The true stems of Costus are substantial enough to look like sugar cane. When I showed a picture of this plant to a Panamanian friend, he immediately said, “Caña agria.” “Caña agria means “bitter cane” and Rowlee reported that Costus were called bitter cane at that time, in 1922.

Costus are Monocots

Flowering plants are divided into two great groups traditionally called monocots and dicots. Wikipedia has such a great description of the value of monocots that I can’t resist quoting extensively:

Monocots comprise the majority of agricultural plants in terms of biomass produced. There are between 50,000 and 60,000 species within this group…. The largest family in this group (and in the flowering plants as a whole) by number of species are the orchids (family Orchidaceae), with about twenty thousand species. The economically most important family in this group (and in the flowering plants) are the grasses, family Poaceae (Gramineae). These include all the true grains (rice, wheat, maize, etc.), the pasture grasses and the bamboos…. Other economically important monocot families are the palm family (Arecaceae), banana family (Musaceae), ginger family (Zingiberaceae) and the onion family Alliaceae, which includes such ubiquitously used vegetables as onions and garlic.

Many plants cultivated for their blooms are also from the monocot group, notably lilies, daffodils, irises, amaryllis, orchids, bluebells and tulips.

Costus are in the order Zingiberales

Current taxonomic systems usually place monocot plants in the class Liliopsida. Within that class is the order Zingiberales, which includes “… horticulturally and economically important plants such as the banana (Musaceae), bird-of-paradise (Strelitziaceae), and edible ginger (Zingiberaceae).” (Wikipedia)

Costus are in their own family, the Costaceae

Costaceae have fused infertile stamen, which form a large petalloid labellum – it looks like a tongue – that often functions to attract pollinators. In the image on the left, below, you can barely see the labellum in the center of the flower. In the image on the right, the plant is saying “Ah,” and you can see it a bit better.

The flowers in this family are generally solitary or aggregated in inflorescences. Here the inflorescence is at the head of the stem. It consists of bracts protecting the petals. Only one flower emerges at a time. You can see the small yellow buds of the next flowers.

This plant, the “porcupine costus” was identified for me by David Skinner at GingersRus. It’s full scientific name is Costus villosissimus Jacq. The stiff hairs on its stem, bracts, and other parts are described as “villose,” hence the name. The species is widespread from Nicaragua to parts of western South America, but is most common in Panama and parts of Costa Rica.

Costus villosissimus has bright yellow flowers. My camera is old enough that it can’t adjust very well to light conditions, and my Photoshop skills are nonexistent, so the above images don’t reveal the true color. I decided to bring a flower home with me and photograph it next to an Allamanda, which is a very common flowering trumpet vine in the area. Anyone who has seen an Allamanda will know instantly the color of the Costus villosissimus. It’s almost identical. Frustrating that the light conditions on our work bench are so much better for capturing true color than the conditions in the woods! (Costus villosissimus on the left below, Allamanda on the right).

Several species of Costus in the New World tropics are pollinated by hummingbirds or orchard bees (Kay, et al. American Journal of Botany). Nearly every morning I hear the buzz of a bee near this plant, but the one day I saw one (a big black fellow) I did not have my camera with me. However, at another time, I did get to watch this other creature for awhile. (You’ll have to click on the images to enlarge them.) He or she may have been looking for nectar outside the flower, among the bracts. But that’s a story for another day.

5 August 2007 Update: I’ve now seen another definite young Costus villosissimus plant along my walk – about 200 m from this one. Here it is:

Coincidentally, the view of this young plant makes it easier to see the spiral arrangement of the leaves along the stem. The portion within the rectangle in the image above is shown below, with the leaf stalks (petioles) highlighted in red. I think the spiral is pretty clear this way.

At any rate, there are also a couple more, smaller plants along the trail that might also be Costus. I’m keeping an eye on them.  It would certainly be nice to have that section of the trail ornamented with several  Porcupine Costus plants!