鸢尾属31个分类群的花粉形态及其分类学意义

Pollen morphology of 31 taxa of genus Iris(Iridaceae)and its taxonomic implications

关键词:  鸢尾属, 临界点干燥法, 花粉形态, 分类学意义, 扫描电镜

Key words:  Iris, critical-point drying method, pollen morphology, taxonomic implications, SEM

摘要:

为研究鸢尾分类群的花粉形态及其潜在分类学意义,以鸢尾属3个亚属的31个分类群的花粉为材料,采用临界点干燥法对供试材料的花粉形态进行扫描电镜观测和系统聚类分析。结果表明:(1)31个分类群的花粉均为异极单粒花粉,花粉大小中等或大,扁球形、近扁球形或圆球形; 远极沟膜光滑或具纹饰膜; 花粉外壁具半覆盖层或无覆盖层,外壁纹饰通常为不同类型的异型网状,少数为芽孢状-杵状。(2)粗根鸢尾的花粉无萌发区,其余类群的花粉粒具远极单沟; 在大苞鸢尾、矮鸢尾和囊花鸢尾花粉粒中发现具环状远极沟的花粉; 在胡氏鸢尾的花粉粒上发现双极沟现象,这在鸢尾属中为首次报道。(3)系统聚类分析显示,平方欧氏距离为10时,31个鸢尾分类群的花粉聚为西伯利亚鸢尾型、德国鸢尾型、短旗鸢尾型、紫苞鸢尾型、燕子花型、琴瓣鸢尾型和粗根鸢尾型7类,参试分类群基本按照形态分类学的亚属、组和系的关系聚类; 7个类型中,德国鸢尾型的花粉粒最大,紫苞鸢尾型的花粉粒最小; 短旗鸢尾型花粉无覆盖层,外壁纹饰为芽孢状-杵状; 琴瓣鸢尾型花粉为近扁球形,远极沟具纹饰膜。(4)3个亚属花粉形态可能的系统发育趋势为无附属物亚属较有髯鸢尾亚属更原始,紫苞鸢尾系是所研究种类中最原始的类群,野鸢尾亚属和冠饰鸢尾组可能是无附属物亚属向有髯鸢尾亚属过渡的中间类型。(5)临界点干燥法和2,2-二甲氧基丙烷(DMP)直接法是适宜鸢尾属植物花粉材料制备的方法。该研究结果表明31个鸢尾属分类群花粉形态具有一致性和差异性,孢粉学特征可作为属内划分亚属、组和系的辅助手段。

Abstract:

To investigate the pollen morphology and its potential taxonomic implications for genus Iris L.(Iridaceae), the pollen grains from 31 taxa across three subgenera of Iris were used as materials. The materials were prepared using critical point drying method, followed by scanning electron microscopy(SEM)observation and systematic cluster analysis of pollen morphology. The results were as follows:(1)All the pollen grains of the 31 taxa were monad and heteropolar, oblate, suboblate or spheroidal in shape, with medium or large size. The sulcus membrane was smooth or ornamented. The pollen grains were semitectate or atectate, with different types of heterobrochate(rarely gemmate-clavate)exine ornamentation.(2)The pollen grains of Iris tigridia were inaperturate, while those of the remaining taxa were sulcate. Zonasulcate pollen grains were found in I. bungei, I. kobayashii and I. ventricosa. For the first time the disulcate pollen grains were found in I. hookeri in genus Iris.(3)Cluster analysis showed that at a squared Euclidean distance of 10, 31 taxa could be clustered into seven types, i.e., Sibirica type, Germanica type, Pumila type, Ruthenica type, Laevigata type, Spuria type and Tigridia type. The taxa studied cluster basically in accordance with the subgenera, sections and series of the morphotaxonomy. Of the seven types, the Germanica type had the largest pollen grains and a heterobrochate reticulate exine with the largest lumina, while the Ruthenica type had the smallest pollen grains and a microreticulate or nanoreticulate exine. The Pumila type was characterized by atectate pollen grains with a gemmate-clavate exine ornamentation and the Spuria type was characterized by suboblate shape pollen grains with an ornamented sulcus membrane.(4)The possible evolutionary trends of the pollen morphology of three subgenera were proposed: the subgenus Limniris was more primitive than the subgenus Iris, series Ruthenicae was the most primitive taxon among the species studied, and subgenus Pardanthopsis and section Lophiris could be the intermediate types in the transition of the subgenus Limniris to the subgenus Iris.(5)The critical-point drying method and 2,2-dimethoxypropane(DMP)direct method were suitable methods for the preparation of pollen micromorphology of the genus Iris. The results of this study indicate that the pollen morphology of 31 Iris taxa reflects both consistency and differences. The morphology data of pollen can be used as supplementary characteristics to identify the subgenera, sections and series, providing reliable palynological evidence.