| Summary: | 博士 === 國立臺灣大學 === 森林學研究所 === 70 === An attempt has been made to (1) . study the biological characters and life history of Taiwania which are urgently needed in forestry; and (2), evaluate the overall phenetic affinities among the genera of Taxo-iaceae, with special reference to the genus Taiwania.
Biosystematic characters in the important stages of life history were thoroughly investigated on Taiwania cryptomerioides. The observa-tions made include those of geographical distribution, general habitat and habit, leaf morphology and anatomy, histology of shoot apex, stem and wood anatomy, microsporangiate and megasporangiate strobili, micro-sporogenesis and male gametophyte, megasporogenesis and female gameto-phyte, fertilization, embryogeny, seed morphology and cytological evidences. All the ten genera of Taxodiaceae were adopted as operational taxonomic units(OTU''s ) in the numerical analysis. A total of 190 unit characters was chosen for the comparison of overall phenetic affinities among the OTU''s. These data were gathered from the present observations on Taiwania in addition to those from available literatures for other genera of the same family. Computations were carried out from the data matrix to produce a matrix of coefficients of similatiry between any two taxa. Cluster analysis was conducted to yield a dendrogram representing the systematic hierarchy of the family. The evaluations of generic relationships and the taxonomic status within Taxodiaceae have been made basing on the similarity coefficients and the clustered dendrogram.
The systematic observations revealed that Taiwania shows many typical characters of the family Taxodiaceae. The major deviation from the normal characters of the whole family is the megasporangiate strobilus or seed cone. Taiwania is much distinghished for its simple external structure of the bract-seed scale complex (cone scale). It represents the ultimate reduction of sporophylls and the total fusion of bract with the sterile component of seed scale complex (ovuliferous scale). However, the compound nature of cone scale is still evidenced in vascular anatomys well as in fossil remains. since a series of reduction and fusion of the scale components develops in various genera or even in a single enus of Taxodiaceae, this criterion is not valid in treating Taiwania is a distinct family, as has been pointed out by some taxonomists.
The study of life history showed that there are a resting phase and two active growth phases in the vegetative shoots of Taiwania. To complete a reproductive cycle, it requires nearly 14 months. Both male and female strobili are initiated in late summer or early autumn of the current year. The megasporangiate strobilus has a quite distinct restlng stage towards the end of the year, while the microsporangiate strobilus has less obvious resting stage. Activities resume in late January or early February in the next spring. The pollination takes place in late February or early March. The fertilization is observed conducting in late June. The seeds are mature in late september and shed in the subsequent two months.
Considering the overall phenetic relationship,Taiwania is a rather typocal genus of Taxodiaceae. In the grouping of tribes made by pilger & Melchior (1954), Taiwania was regarded as most related to Athrotaxis and was included in the tribe Athrotaxeae. However, it has a closest affinity with Sequoiadendron as revealed by the present study.
Through careful comparison of the Taiwan plants with the specimens from Mainland China and Burma, it is concluded that there is only one valid species of Taiwania . The two additional species , namely Taiwania flousiana Gaussen and T. yunnanensis Koidzumi, should be relegated to the synonyms of the originally proposed species, i. e.Taiwania cryptomerioides Hayata.
The genus Sequoiadendron has the highest index of typicality in the whole family ,suggesting that it is the most typical genus and possesses the normal characters of the family in a largest proportion. Genera such as Glyptostrobus, Cryptomeria and Taiwania come next in similar gradings. They have mean similarity very close to that of Sequoiaden-dron, However, the nomenclatural type genus,Taxodium, is graded quite low, not representing the most btypical one.
Basing on the dendrogram resulted from cluster analysis, the phenon line at 0.637 similarity level is able to divide Taxodiaceae into two ubfamilies . The smaller subfamily, sciadopitoideae, contains the sole enus Sciadopitys; while the larger one, Taxodioideae, includes all other enera of the family. Further tentative groupings within Taxodioideae an yield 5 tribes at 0.725 similarity level. of the five tribes, they are Taxodieae (Cryptomeria, Glyptostrobus and Taxodium),Taiwanieae (Taiwania and Sequoiadentdron ), Athrotaxeae (Athrotaxis ), Cunninghamieae (Cunninghamia), and Sequoieae (Sequoia and Metasequoia). Nevertheless, there are no large and easily defined gaps in teh dendrogram under this subfamily in such a tentative scheme. A nested analysis of variance for the mean similarity values in the whole family has been conducted to evaluate the hierarchical. classification of subfamily, tribe and genus. It reveals that the subdivision of two subfamilies is significant,while the grouping of tribes under subfamily Taxodioideae is not valid. The tentatively proposed tribes show relative affinities among the 9 component genera, but they yield little comprehensive and useful concepts.
It is believed that the evolution of taxodiaceous complex has passed its climax and the extant plants are relic foums representing many separted lines of modification. Certainly the taxodiaceous plants have many outstanding characters capable of uniting them in the same family. However, they are also found having some considerably distinghished characters of their own. Thus it is difficult to group them into distinct taxa such as the tribes. This it is clearly confirned by the tentative grouping using cluster analysis. In the clustered dendrogram, a slinght change of the level of critical phenon line will result in different combinations of tribe. Such division of tribes is likely to diversify according to different authors using various but ambiguous criteria. Since the pecularity of taxodiaceous plants has already been expressed in teh works treating many monotypic genera by tanonomists concerned, further grouping of tribes are insignificant and inconvenient. In the conclusion of evaluations it seens that to make a formal proposal of tribes in the family Taxodiaceae is not quite suitable, while the recognization of twothe subfamilies is justified as it has already appeared in the earlier treatise of pilger(1926).
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