A Neotropical Savanna

 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.

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Here are three red and yellow plants, from left to right, an orchid (Epidendrum radicans), a milkweed (Asclepias curassavica), and a roadside weed (Lantana camara). They all grow in our back yard, although the orchid is there only because I put it there.

If you compare these plants in pairs, you’ll find other features besides color in common. The orchid and the milkweed package their pollen in little sacs called pollinia. The milkweed and the lantana produce nectar (the orchid does not), are not indigenous to Central America (the orchid is), and can be toxic to herbivores. All three are said to bloom year-round, but only the lantana does so in our backyard. All three are said to have the same pollinators, which brings us to the fame this group of plants has among some students and some botanists.

It has been suggested that they belong to a “floral mimicry complex.” But do they? And what is a floral mimicry complex, anyway?
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