Cyathia of Euphorbia spathulata (Euphorbiaceae) Possess Both Cleistogamous and Chasmogamous Modes of Pollination


Christian Rabot

Additional Authors:

W. John Hayden



morphology, Cyathium, Euphorbia spathulata,

ABSTRACT Cyathium morphology of Euphorbia spathulata from three populations in central Virginia was studied from early developmental stages through nominal anthesis, defined by exposure of the cyathium to the external environment by divergence of paired subtending cyathophylls. Observations were made via dissecting microscope, compound light microscope sections, and scanning electron microscopy. The plants studied revealed a consistent pattern of asynchronous stamen and pollen development as well as a series of predictable changes in style and stigma orientation. Initially, styles and stigmas of pistillate flowers maintain a near-axial (erect) position. Later, when still enclosed by subtending cyathophylls, styles reflex, placing stigmas near early developing anthers shedding pollen. Pollen grains observed on stigmas at this stage indicate cleistogamous pollination. Eventually, paired cyathophylls diverge, exposing the cyathium to the external environment; at this stage, styles and stigmas assume an ascendant position as late-maturing anthers shed pollen, a configuration conducive to chasmogamous pollination. These observations indicate that a succession of cleistogamy and chasmogamy characterize the reproductive process of each cyathium of E. spathulata, at least in the populations studied.