台灣產桫欏科植物配子体與幼孢子体的形態

Morphology of the Gametophytes and Young Sporophytes of Cyatheaceae Native to Taiwan

台灣產七種桫欏科植物中，筆筒樹、韓氏桫欏、台灣樹蕨、與鬼桫欏之每個抱子囊有64顆孢子，而南洋桫欏、台灣桫欏及蘭嶼筆筒樹則有16顆孢子。除了韓氏桫欏與台灣樹蕨外，孢子發芽都屬「桫欏型」，韓氏桫欏與台灣樹蕨之孢子發芽時，假根形成較延遲。七種植物之配子體發育型式均為「槲蕨型」，但每種均有少數以「鐵線蕨型」發育。多細胞之鱗片狀毛發生在中肋的腹背兩面，並隨年齡增長而加大體型，此種多細胞之鱗片狀毛為桫欏科植物所特有。第一至第三或四片幼孢子葉無中肋，單列至多列及棍棒狀多細胞毛混生於桫欏屬之幼孢子葉上，但筆筒樹之幼孢子葉則缺棍棒狀多細胞毛，此或可為系統發生上分離之一證據。此外，孢子囊內具16或64顆孢子之特徵也反應桫欏屬植物在演化上的兩個事件。

Seven species of Cyatheaceae are native to Taiwan. Sphaeropteris lepifera, Alsophila denticulata, A. metteniana, and A. podophylla produced 64 spores per sporangium, whereas A. loheri, A. spinulosa, and A. fenicis produced 16 spores per sporangium. Spore germination was Cyathea-type, except in A. denticulata and A. metteniana. In these two species, the rhizoid formation was delayed. Gametophytes of all seven species usually underwent Drynaria-type development, but a few gametophytes of all seven species exhibited Adiantum-type development. Multicellular, scale-like hairs on the dorsal and ventral surfaces of the midrib cushion increased in size and changed shape with age. These scale-like hairs distinguish Cyatheaceae gametophytes from the gametophytes of other fern families. The first three or four fronds of young sporophytes lacked midribs. Uniseriate to multiseriate and club-shaped pluricellular hairs were intermingled on the fronds of juvenile sporophytes of all six species of Alsophila. The lacking of club-shaped pluricellular hairs on Juvenile sporophytes of S. lepifera supports the taxonomic separation of Sphaeropteris from Alsophila. The presence of 16- and 64-spored sporangia suggests two evolutionary events within Alsophila.