British plants in the rubiaceae (bedstraw, or madder family) are easily identified by their four-angled stems, whorled leaves and small, four-petalled flowers (less often five-petalled), generally coloured white or yellow. Flowers can be solitary, growing at the leaf nodes, but are usually arranged in open, branched clusters. Flowers have the same number of stamens as petals. Seventeen species grow in the British Isles.