摘要
海草是指那些只生长在海洋中的水草，不包括咸淡水生的类型在内(最近通过判别分析，证明这样划分是正确的)。虽然海草是一个生态类群，而不是一个分类单元，但是搞清楚海草的系统分类，无疑是海草学研究中的一个不可缺少的环节。
The purpose of this article is to investigate some numerical methods for the systematic taxonomy of seagrasses. The taxonomy of seagras-ses like that of the other angiosperms is based mainly on characteristics of their generative structures. Regrettably these structures are not often found in most seagrasses, and in some species they are not known at all or known only incompletely. This means that the bulk of herbarium materials is sterile, especially as a prioriweight ing used by some morphological taxonomists, there are, however, many questions arose. Therefore we decide to make some remarks on the delimitation and subdivision of seagrasses by means of numerical taxonomy.In this paper three methods of clustering are used.i) Regard b + c as the measure of the degree of similarity between Qi and Qj and cluster by the minimum distance method.ii) Regard the information increment Ai + j as the measure of the degree of similarity between Qi and Qj and cluster by the information classification method.iii) The corresponding analysis; sum up the results from three meth ods and give the new system of classifying for seagrasses.The results of i) and ii) agree closely to each other, which are given as two dendrograms (Fig 1 ).Twel vr genera of seagrasses are shown clear ly to have 5 discontinuous groups. The similarity coefficients of distance and information,after rearrangement, present a similar situation.Based on the data from each ten characteristics, the seagrasses can be subdivided into five families. They are Zosteraceae (including Zostera, Phyllospadix and Halodule), Thalassiaceae (including, Thalassia and Halophila), Amphibolisaceae (including Amphibolis, Thalassodendron and Heterozostera), Posidoniaceae (including Posidonia, Cymodocea and Syringodium) and Hydrocharitaceae (only including Enhalus).The result of corresponding analysis shows that the first component accounts for 40 per cent of the total variability, and the next two components for 27 and 16 per cent respectively.In the first and second components, X10 (the method of pollination) and X3 (with or without tannin cells) have respectively the largest reading.Hydrophilous pollination is important requirements for seagrasses life in the sea.Entirely submerged pollination takes place in most genera, they are Halophila, Halodule, Cymodocea, Syringodium, Amphibolis, Thalassodendron, Posidonia and Thalassia. Semi-aquatic surface pollination has been recorded for Phyllospadix and Zostera, although entirely submerged occurs just as of ten in these genera. Among the marine Angi-osperms, Enhalus accoraides is the only species which shows aerial surface pollination. This feature is also known from some fresh water forms.With or without tannin cells related directly to the origin of sea-grasses, this fact indicates that it can be accepted as an important characteristic for selection weighting.
