Megagametophyte development, fertilization, and cytoplasmic inheritance in Taxus brevifolia

Taxus brevifolia is a tree of evolutionary and medicinal importance. This study describes the megagametophyte development, archegonial development, and fertilization in this species. In Victoria, British Columbia, megasporogenesis and free nuclear mitosis within the megagametophyte occur anytime between early February until the end of June. Within the differentiated sporogenesis tissue, a megaspore mother cell develops and undergoes meiosis, usually forming a linear tetrad of megaspores. Though up to three of the megaspores may be functional, the chalazal megaspore develops faster than the others and is usually the functional megaspore. Cellularization of the megagametophyte begins in mid-April and continues until early June. The presence of an ephemeral ventral canal nucleus was confirmed. Fertilization was observed in June 1996. The mature egg cell cytoplasm and sperm structure are used to infer paternal inheritance of plastids and biparental inheritance of mitochondria. This anatomic and developmental study supports the inclusion of Taxus in the order Coniferales.