印度紅樹林的種子構造與發芽類型及其在分類學上的關係

Seed Structure and Germination Pattern of Some Indian Mangroves with Taxonomic Relevance

本文研究印度17種（隸屬於10科）鹽生植物的種子形態與發芽類型，並探討其傳播、復育及分類上之意義。在研究的物種中，除爵床（Acanthus ilicifolius）、土沉香（Excoecaria agallocha）、海桑（Sonneratia apetala）及木果楝（Xylocarpus sp.）外，果實均只含一種子。有些種子是無法與果實分開的，譬如藍雪科的一種紅樹林植物（Aegialitis rotundifolia）、桐花樹（Aegiceras corniculatum）、海茄冬（Avicennia sp.）、水椰（Nypa fruticans）以及研究的所有紅樹科的物種。這些物種的繁殖體多由潮水所傳播，在定根之前需先漂流相當的距離以逐漸適應鹹水的環境。所有的紅樹科植物均有胎生苗的特性，受精後種子不經休眠逕自萌芽。因此種子還附在母株時，其下胚軸即由種子及果實中延生出來，這種特性在演化的途徑上是較為複雜及特殊的。在傳播時，藍雪科植物、桐花樹、海茄冬及水椰的初生胎生苗，其下胚軸僅穿過種皮而保留在果皮內，這種狀況可視為隱藏式胎生現象。根據種子的特徵，本文還提供檢索表作為鑑別物種之用。

Seed morphology and germination patterns of 17 halophytes belonging to 10 families of Sundarbans, India, were studied in view of their dispersal, rehabilitation and taxonomic interest. Fruits are mostly one seeded in the investigated taxa, except in Acanthus ilicifolius, Excoecaria agallocha, Sonneratia apetala and Xylocarpus spp. Seeds are inseparable from fruits in Aegialitis rotundifolia, Aegiceras corniculatum, Avicennia spp., Nypa fruticans and the investigated species of Rhizophoraceae. Propagules are mostly dispersed by tidal water. They have to float for some distance prior to establishment for a gradual adjustment of the young ones towards the saline environment. Viviparous germination occurs in all members of Rhizophoraceae, where seed germination takes place immediately after fertilization without any dormancy period. In this case the long hypocotyl comes out of the seed and ultimately from the fruit when the fruit is still attached with the mother plant. This phenomenon is considered as the most complex and highly evolved phenomenon in evolutionary line. In Aegialitis rotundifolia, Aegiceras corniculatum, Avicennia spp. and Nypa fruticans, germination occurs following an incipiently viviparous type where the hypocotyl pierces out of the seed coat but not from the exocarp at the time of dispersal. This incident should be defined more appropriately as cryptovivipary. On the basis of seed characters, an identification key was generated for easy identification of the dispersing units.