Studies of protonemal morphogenesis in mosses. XII. Ephemeropsis, the zenith of morphological differentiation

This light and scanning electron microscope study of freshly collected material confirms that the protonemal system of Ephemeropis is the most highly differentiated so far found in mosses and reveals hitherto unsuspected roles for its unique features. Whereas substrate attachment in the Hypnales, illustrated here in Homalothecium sericeum, is by clusters of irregular terminal mucilage-secreting ramifications on long otherwise unbranched rhizoids and in other mosses is via otherwise unmodified rhizoids, the anchoring structures or hapteres in Ephemeropsis are very regular side branch systems that also secrete copious mucilage. This last feature, only clearly visible in living specimens, also invests the bristle-like appendages similarly unique to Ephemeropsis. Abundant cyanobacteria in this mucilage may be an important nitrogen source for Ephemeropsis. Other features most likely linked to growth on twigs, the leaf bases of ferns and tree ferns and epiphylly are the absence of food-conducting cytology from the main protonemal axes and the rapid absorption of water by the much-branched chloronemata. Gemmae are produced at the tips of attenuated filaments that grow downwards in a spiral pattern and are rapidly anchored to the subjacent leaves by means of short side branches at their bases that also secrete copious mucilage.