Excerpts from Jim Conrad's
Naturalist Newsletter

from the February 21,  2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
A PRETTY MAT OF CALLISIA

In parklike areas where the soil is so thin that flat, white limestone bedrock emerges over large areas, nowadays often you find dense mats of the little, white-blossomed, three-petaled perennial shown below:

CALLISIA CORDIFOLIA, plant

That's CALLISIA CORDIFOLIA, usually referred to as Callisia in English, and if its leaves and three-petaled flowers remind you of the above dayflower it's because Callisia belongs to the same family, the Spiderwort Family, the Commelinaceae. You can see a close-up of a flower with its six stamens below:

CALLISIA CORDIFOLIA, flower

This flower is similar to a spiderwort flower (genus Tradescantia), and in fact formerly some botanists placed our species in that genus. You can compare the above picture with the North's Zigzag Spiderwort at http://www.backyardnature.net/n/h/spiderwo.htm.

An important difference between the two plant types is that spiderwort flowers are immediately subtended by large, leaf-like bracts, thus looking "stemless" on the plants, while in the photo you can see that Callisia flowers are held on a slender stem (the pedicel), and that the pedicels themselves arise from a larger stem (the peduncle). Also Callisias are much smaller than Tradescantias, the flower in the photo is less than 1/5th inch across (5 mm). A pretty distinction of our species' flowers is that the three sepals arising below the much larger petals bear striking color markings you'd never see if you weren't on your belly looking up from below them, shown below:

CALLISIA CORDIFOLIA, sepals

So, earlier we had the pleasure of "variations on a dayflower theme." With Callisia we have "variations on a Spiderwort-Family theme." Here we see how within a family the genera can sort themselves out not with the subtle features that distinguish species, but with grosser, more fundamental differences, such as whether large bracts are present below an inflorescence.

The genus Callisia, with its center of evolution here in Mexico, comprises about 20 species, of which seven make it into the Southeastern US. Our Callisia cordifolia occurs from Mexico and Florida south to northern South America.