Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)

ABSTRACT The pollen grains of 15 species belonging to five genera (Ceiba Mill., Eriotheca Schott & Endl., Pachira Aubl., Pseudobombax Dugand, and Rhodognaphalopsis A. Robyns) of the subfamily Bombacoideae (Malvaceae s.l.) were acetolysed, measured, described and photomicrographed under light microscopy and scanning and transmission electron microscopy, in order to characterize the pollen morphology of species of the subfamily occurring in Brazil. The pollen characters studied were size, shape, exine constitution, and apertural type. Pollen grains were medium to large-sized and isopolar with a (sub)circular and (sub)triangular amb with flat, convex or concave sides; oblate to suboblate; 3(-4)-colp(or)ate or 4-5(-6)-colporate, planaperturate, sinuaperturate; equatorial calottes different or not; exine tectate or semitectate, perforate and microreticulate with or without supratectal spines. The results confirm the eurypalynous nature of the group with variation among the studied genera being mainly in the exine pattern.

摘要 本研究对隶属于广义锦葵科（Malvaceae s.l.）木棉亚科（Bombacoideae）下5个属——吉贝属（Ceiba Mill.）、毛葵树属（Eriotheca Schott & Endl.）、瓜栗属（Pachira Aubl.）、假木棉属（Pseudobombax Dugand）以及Rhodognaphalopsis A. Robyns——的15个物种的花粉粒进行乙酰解处理、尺寸测量与形态描述，并分别通过光学显微镜、扫描电子显微镜及透射电子显微镜完成显微成像，旨在表征巴西境内分布的该亚科物种的花粉形态特征。

本次研究观测的花粉性状包括花粉大小、形状、外壁结构及萌发孔类型。所研究的花粉粒多为中等至大型，且为等极花粉，轮廓呈近圆形至近三角形，边缘平坦、凸出或凹陷；形状为扁球形至近扁球形；萌发孔类型为3(-4)孔沟型或4-5(-6)孔沟型，具平萌发孔或弯萌发孔；赤道帽（equatorial calottes）存在与否或存在差异；外壁为覆盖层型或半覆盖层型，具穿孔且呈细网状纹饰，部分覆盖有刺状突起。

本研究结果证实了该类群具有花粉多态性特征，所考察的各属间的形态差异主要体现在外壁纹饰模式上。