Study on external morphological variation and relationship of species, cultivars and hybrids of Taxodium.

According to nine qualitative indexes including canopy shape,needle shape,arrangement and attachment modes of deciduous sprig on lateral branch,arrangement and attachment modes of needle on deciduous sprig,leaf color in growing stage,leaf color in fall and winter,trunk color,growth characteristics and having cone or not,as well as five quantitative indexes including length and width of deciduous sprig,needle length,leaf angle and leaf number per centimeter on deciduous sprig,the variation status of external morphological characters of twenty-seven tree species(including species,cultivars and hybrids) of Taxodium Rich.were observed and compared.On the basis,the cluster analysis was carried on,and a key of the twenty-seven tree species of Taxodium was compiled based on the external morphological characters.The results show that different hybrids not only possess parent's external morphological characters,but also vary in some degrees.In nine qualitative indexes,variation of some indexes(such as leaf color in fall and winter,growth characteristics,etc.) is greater,but that of needle shape,arrangement and attachment modes of deciduous sprig on lateral branch,etc.is smaller.The five quantitative indexes among twenty-seven tree species have significant differences(P0.01) with 4.68-11.19 cm of deciduous sprig length,0.59-2.38 cm of deciduous sprig width,0.84-1.84 cm of needle length,24.1°-52.9° of leaf angle and 6.3-16.0 of leaf number per centimeter on deciduous sprig.The twenty-seven tree species have been divided into five groups by cluster analysis: T.distichum(L.) Rich.,T.mucronatum Tenore and T.'Zhongshansha 9' are independent groups,respectively;T.ascendens Brongn.,T.ascendens 'Nutans',T.'Zhongshansha 91',T.'Zhongshansha 102' and T.'Zhongshansha 401' are clustered together;T.distichum 'Pendens',T.distichum 'Fastigiata',T.'Zhongshansha 1',T.'Zhongshansha 24',T.'Zhongshansha 27',T.'Zhongshansha 46',T.'Zhongshansha 86',T.'Zhongshansha 118',T.'Zhongshansha 136',T.'Zhongshansha 140',T.'Zhongshansha 146',T.'Zhongshansha 149',T.'Zhongshansha 302',T.'Zhongshansha 405',T.'Zhongshansha 406',T.'Zhongshansha 407',T.'Zhongshansha 501',T.'Zhongshansha 502' and T.'Zhongshansha 503' are clustered as another group.It is suggested that the result of cluster analysis based on external morphological variation can reflex the relationship among species,cultivars and hybrids of Taxodium to a certain extent.