半边莲亚科（学名：lobelioideae）也叫山梗菜亚科，约20属375余种，主要分布在热带和暖温带。中国有3属24种，生长在长江以南地区。

本科植物多为草本、灌木，也有一些乔木品种，植株常含乳汁；单叶互生，少对生或轮生，无托叶；花两性，单生，两侧对称，花瓣5，合瓣，雄蕊着生在花筒上。

1981年的克朗奎斯特分类法将其中各属纳入桔梗科，1998年根据基因亲缘关系分类的APG 分类法将其单独分出一科，但认为可以和桔梗科选择性地合并。

Lobelioideae is a subfamily of the plant family Campanulaceae. It contains 32 genera, totalling about 1200 species. Some of the larger genera are Lobelia, Siphocampylus, Centropogon, Burmeistera and Cyanea.

They are perennials, sometimes annuals, ranging in form from herbs to small trees. Most species are tropical in distribution, but in total this subfamily occurs almost worldwide, being absent only from Arctic regions, central Asia and the Near East.