Tithonia rotundifolia

I never thought I’d use the genus and species name of a plant for my title with such confidence (95%, as they say). But here it is.

[A high resolution image is here. ]

Tithonia is named for Tithonus, a Trojan in Greek mythology who was allowed to be immortal but was not granted eternal youth and who, after becoming very ancient, was turned into either a grasshopper or a cicadia. The species name, rotundifolia, means “round leaf,” which would shake my confidence in the scientific name if I didn’t have lots of other criteria for deciding on it. You’ll find picture of the leaves after the break.

 

The leaves on this plant have two forms. The smaller ones are oval with a pointed tip and with toothed edges. The larger ones have 3 lobes. The leaf blade is “decurrent” on its stem, which means that the blade extends down the stem some from the point where it attaches. You can see this pretty clearly on the leaf to the right of the lower flower.

The characteristic that makes this plant a member of the Asteraceae family is, to use the words of Thomas Elpel: “composite flowers in disk-like heads.” (Elpel’s page in his Wildflowers and Weeds web site that describes the Aster family is a must-read for those who, like me, are new to plant identification and want to get acquainted this large family.)

The disk-like heads are made up of very small flowers, often called florets. The rays surrounding the disk are themselves flowers. In T. roundifolia, the ray flowers are golden with a tiny notch at the end.

 

In this image you can see both brown-black and yellow-orange florets. These are the anthers (male, brown-black) and stigmas (female, yellow-orange) parts. You may be able to see the details better in the high resolution image here.

The plant itself is a large shrub. I saw several shrubs on this roadside corner, but only one is pictured:

The reason I have such confidence in the scientific name of this plant is because a new and wonderful book has arrived in our household: A Guide to the Tropical Plants of Costa Rica by Willow Zuchowski. It’s 529-pages-worth of botanical, environmental, and social detail about the plants of the area. Since this neotropical savanna where I live is only a few miles from the Costa Rican border, nearly every page of the book has something familiar on it.

So I’ve learned, for instance, that T. rotundifolia is found mostly on the Pacific slope between 300 and 1,000 m (check – we’re at about 800 m), it’s an herb that grows as a shrub 1-4 m tall (check), it flowers along roadsides (check), and it flowers and fruits from late October through January (check – well, it’s not late October yet, but they did just start blooming). It may be coincidence, by the way, but I just read today that two Boston University professors have shown that flowers in the Concord area are blooming 11 days earlier now than they did in Thoreau’s time.

A final, nice surprise. T. rotundifolia is related to the Mexican sunflower (T. diversifolia), which has been used in Africa as a green manure crop. A brochure on how to use it is here. The differences between the two species are: the flower head of T. rotundifolia is smaller (about 7 cm across) than that of T. diversifolia (about 14 cm across), and the flowerhead bracts that form a cuplike receptacle are pointed in T. rotundifolia and rounded in T. diversifolia.