台灣海桐屬植物的解剖研究

Abstract

中文摘要 海桐科僅分佈於舊世界，台灣則僅產海桐屬，包括五種及一變種。分佈自低海拔(海桐、七?香及蘭嶼海桐)經中海拔(部份疏果海桐)至高海拔(疏果海桐、細葉海桐及大葉海桐)。其中僅栽培之七?香可成為小喬木者，餘為或高或矮之灌木，包括野生的七?香。於生育習性上，台灣的海桐屬植物均屬中生習性偏旱生習性者，其爭執性比值與中生型比值於海桐科植物內均屬低者。高山種類的低比值主要源於冬季高山常有凍霜的現象，因而引起植物體生理上的乾旱；葉內柵狀組織面積對細胞間隙的比值均低，但僅大葉海桐具有較厚的角皮層。平地種類者之低比值，則多源於高溫，多陽及夏季常有長期乾旱的結果；葉則大多具有較厚之角皮層. 花部解剖研究的結果顯示，大葉海桐的解剖特徵最為穩定；疏果海桐的變異最大，於花器數及心皮數均有退化之現象。就整體特徵言，萼跡的變異最大，但基本型應為三脈跡共同起源者；合生心皮數有由三往二之傾向。僅七?香較成熟的花之子房下端呈中軸胎座型，且由於心皮腹脈均不為倒轉的維管束，因此推論此中軸胎座應由側膜胎座而來。基於形態上，解剖上的證據以及地理上的參考證據，建議提出兩個亞種：Pittosporum pentandrum subsp. formosanum以及 P. tobira subsp. calvescens。

英文摘要 Pittosporaceae is exclusively native to the Old World. There is only one genus, Pittosporum, of five species and a variety in Taiwan. They are found from low-land (P. tobira, P. pentandrum and P. moluccanum), through median altitude (P. illicioides in part) to high altitude (P. illicioides, P. illicioides var. angustifolium and P. daphni-phylloides). Except the cultivated P. pentandrum will grow into a small tree, most species of Formosan Pittosporum, including the wild P. pentandrum, are small or large shrubs. As to the habit, they are all mesomorphic but more or less tend to be xeromorphic. In Pittosporaceae as a whole, both the values of vulnerability ratio and mesomorphy ratio of Formosan Pittosporum are low. In the alpine species, all species are with low value of ratio of palisace tissue to intercellular space, but only P. daphniphylloides with thick cuticle. Thus, the low figures of both ratios may reflect a form of physiological drought, caused by the winter frost. As for the low-land species, with more thick cuticle, the low figures of both ratios may be caused by high temperature, sunny and long period of drought in summer. From the study of floral anatomy, the anatomical characters in P. daphniphylloides are most stable, but show considerable diversity in P. illicioides, with reduction of both floral organs and number of syncarpous carpells. In all characters as a whole, the sepal traces show the most diversity, and the basic type is 3-traced, the number of syncarpous carpells is reduced from three to two. Occasionally, the ovary is 2-celled in the base and /or apes, but most placentae arc parietal. Only in the much mature ovary of P. pentandrum, the axile placentation can be observed. Since all the carpellary ventral bundles are not inverted, it is supposed that the axile placentation was derived from parietal one. Based on morphological, anatomical and geographical evidences, two subspecies, i.e. P. pentandrum subsp. for- mosanum and P. tobira subsp. calvescens can be proposed.