SEXUAL REPRODUCTION AND THE LIFE-HISTORY OF SPLACHNIDIUM-RUGOSUM (PHAEOPHYCEAE)

Sexual reproduction in Splachnidium rugosum is anisogamous. Sporophytes produce unilocular sporangia in conceptacles. In culture, zoospores developed into filamentous gameto- phytes which remained sterile but occasionally gave rise to sporophytes directly. Wild gametophytes become fertile during spring and summer. They are dioecious and bear conical plurilocular gametangia. Male gametangia are distinguished from females by their orange colour and smaller loculi, Male gametes are smaller than female gametes and possess a smaller chloroplast with a more conspicuous eyespot. Plasmogamy occurs rapidly after female gametes have settled and withdrawn their flagella. Female gametes are capable of parthenogenesis and develop into more female gametophytes. Male gametes germinate but fail to develop beyond a few cells. Chromosome counts gave 20-24 for wild sporophytes and eight-10 for wild gametophytes, and it is inferred that meiosis occurs in unilocular sporangia. During sporogenesis, the characteristic stellate chloroplast with an internal pyrenoid temporarily assumes a simpler form with a lateral pyrenoid. © 1991 Taylor & Francis Group, LLC.