马齿苋科(Portulacaceae) 双子叶植物，约19属，580种，广布于全球，美洲最多。肉质草本或亚灌木；叶互生或对生，全缘；花两性，辐射对称或左右对称；萼片通常2；花瓣4－5，稀更多，常早萎；雄蕊4至多枚，通常10枚；于房1室，上位或半下位至下位（Portulaca），有胚珠1至多颗，生于基生的中央胎座上；果为一蒴果。盖裂或2－3瓣裂。

APG II植物分类系统 (2003; 从1998年APG系统未改变的)分配它到核心真双子叶植物分支石竹目。2009年，被子植物APG III分类法从马齿苋科中分出三个独立的科，分别是土人参科（Talinaceae） 、回欢草科（Anacampserotaceae）和小鸡草科（Montiaceae）。

The Portulacaceae are a family of flowering plants, comprising about 20 genera with about 500 species, ranging from herbaceous plants to shrubs. The family has been recognised by most taxonomists, and is also known as the purslane family; it has a cosmopolitan distribution, with the highest diversity in semiarid regions of the Southern Hemisphere in Africa, Australia, and South America, but with a few species also extending north into Arctic regions. The family is very similar to the Caryophyllaceae, differing in the calyx, which has only two sepals.