The plants can grow solitary or can be clump-forming. Many species have firm, tough, fleshy leaves, usually dark green in colour, whereas others are softer and contain leaf windows with translucent panels through which sunlight can reach internal photosynthetic tissues. Their flowers are small, and generally white. Though they are very similar between species, flowers from the species in section Hexangulares generally have green striations and those from other species often have brown lines in the flowers. However, their leaves show wide variations even within one species.