Timing of Reproduction in Hymenopappus tenuifolius Pursh (Compositae), a Purported Biennial

Abstract

As in many other supposed species, the life history of Hymenopappus tenuifolius is best described as short-lived and semelparous, rather than biennial. No individuals in a Texas population of H. tenuifolius successfully flowered at the age of 1.5 years, or after 2 growing seasons. Most plants did not flower until they were 2.5, 3.5, 4.5 years of age or older. Some plants at least 4.5 years old have still not flowered. Hence, H. tenuifolius is not a strict biennial, as previously described. Timing of reproduction in H. tenuifolius is more dependent on individual plant size than plant age. Plants which do flower are usually larger than individuals of the same age which do not flower. Perhaps, in order to reproduce successfully, a certain amount of energy must be available in the taproot to provide the initial investment in the tall flowering stalk characteristic of so many biennial (short-lived semelparous) plant species.