Observations on the mature gametophyte of Phylloglossum (Lycopodiaceae)

Mature, gametangia-bearing photosynthetic gametophytes of Phylloglossum can be grown from the nonphotosynthetic, cylindrical, negatively gravitropic i mmature stages in illuminated axenic culture on a nutrient medium with or w ithout 0.2% glucose. The gametangial-bearing region of these gametophytes, the photosynthetic crown, grows horizontally from the apex of the immature cylindrical stage. At maturity the photosynthetic crown is thickened and bi laterally symmetrical. It is usually narrow and bean-shaped with dorsal and ventral regions. Occasionally, the ventral region becomes thicker and the crown is deltoid in cross section. The dorsal edge or ridge of the crown is the gametangial region with archegonia and antheridia. The gametangia are often hidden because they are interspersed among numerous uni- or bicellula r paraphyses. The lateral surfaces below the gametangial region lack outgro wths, and the ventral region is covered with long rhizoids. The apical meri stem at the anterior end of the crown is overarched by the developing dorsa l tissue of the gametangial ridge. The lower derivatives of the meristem fo rm the ventral region with rhizoids. Phylloglossum gametophytes are unusual because their mode of organic nutrition changes from mycorrhizal to photos ynthetic during ontogeny.