运用比较形态学和比较解剖学方法,使用扫描电镜和光学显微镜对紫花苜蓿复合体(Medicago sativa complex)6 个分类群的叶片形态特征和叶片解剖结构进行了观察和比较,并以15 个叶片表征形态性状为基础,采用聚类分析法(UPGMA)和主成分分析方法(PCA)对6 个分类群进行了数量分类研究。观察结果表明:各分类群叶片的上、下表皮多为不规则形细胞;垂周壁呈深浅不一的波状;气孔器为不规则型,具有蜡质气孔盖,气孔密度有一定差异。6 个分类群的叶片均为薄纸质型,厚度130 ~ 170 μm,表皮细胞切面近圆形或近长方形;栅栏组织细胞1 ~2 层,厚度41 ~68 μm,细胞排列紧密;海绵组织厚度32 ~75 μm,细胞排列疏松;不同分类群叶片的组织疏松度和组织紧缩度有一定的差异,大花苜蓿(M. trautvetterii Sumnev.)叶片的组织疏松度最高,紫花苜蓿叶片的组织紧缩度最高。UPGMA 结果显示:在结合线1. 53 处可将6 个分类群划分为2 支,其中,黄花苜蓿(M. falcata L.)独立为一支,其余5 个分类群聚成另一支;在结合线1. 18 处,第2 支又被分成2 个亚支,其中一个亚支包含紫花苜蓿和天山苜蓿(M. tianschanica Vassilcz.),另一个亚支则包含西锡金苜蓿(M. schischkinii Sumnev.)、座垫苜蓿(M. rivularis Vassilcz.)和大花苜蓿。PCA 结果表明:对紫花苜蓿复合体而言,叶片表皮细胞形状、垂周壁式样、轴性分化特征、组织疏松度和气孔密度等特征具有较好的分类价值;基于主成分分析的Q 分布图与聚类分析结果也具有较高的一致性。根据本研究结果及前人的研究结果,认为国产的紫花苜蓿复合体应包含3 个分类群,即紫花苜蓿、黄花苜蓿及多变苜蓿(M. varia Martyn)。此外,西锡金苜蓿、座垫苜蓿、天山苜蓿和大花苜蓿等杂交后代分类群的性状分化不稳定,应属于多变苜蓿的同种异名植物。

Using methods of comparative morphology and comparative anatomy, the morphological characters and anatomical structures of leaf of six taxa in Medicago sativa complex were studied by SEM and LM. And based on fifteen characterizations, numerical classification of the six taxa was also carried out by means of UPGMA and principal component analysis (PCA). The observation results show that leaf upper and lower epidermis cells of the six taxa are mostly irregular; anticlinal walls appear waved with different degrees; stomatal apparatus is the irregular type with a waxy cap, and the stomatal density varies to a certain degree. The six taxa all have papery leaf with a thickness of 130-170 μm, and the section shape of epidermal cells is subrotund or sub-rectangular. There is 1-2 layer cell in palisade tissue with a thickness of 41-68 μm and compact cell arrangement. The spongy tissue is with a thickness of 32-75 μm and loose cell arrangement. There is a certain difference in leaf structure loose ratio (SR) and structure tense ratio (CTR) among different taxa, in which SR of M. trautvetterii Sumnev. leaf is the highest while CTR of M. sativa leaf is the highest. The UPGMA result shows that the six taxa can be classified into two branches at the combining line of 1. 53, in which one branch is M. falcata L. and other five taxa combine to form. another branch. The latter branch can be further divided into two sub- branches at the combining line of 1. 18, one contains M. sativa and M. tianschanica Vassilcz., and another contains M. schischkinii Sumnev., M. rivularis Vassilcz. and M. trautvetterii. The PCA result shows that shape of epidermal cells, patterns of anticlinal wall, differentiation characteristics of rhachis, SR and stomatal density of leaf possess high taxonomic value for M. sativa complex. Furthermore, the Q distribution map based on PCA is highly consistent with the UPGMA result. According to both of these results and previous research findings, it is concluded that M. sativa complex in China includes three taxa, namely, M. sativa, M. falcata and M. varia Martyn. In addition, differentiation of morphological characters of hybrid taxa, such as M. schischkinii, M. rivularis, M. tianschanica and M. trautvetterii, is unstable and these hybrids should be categorized as allogenic and synonym plants of M. varia.