Podostemaceae

Small, often moss- or lichen-like herbs that cling directly to rocks in fast-flowing river rapids using a flattened, root-like holdfast, their true leaves and stems reduced almost beyond recognition; tiny flowers emerge briefly above the waterline only when river levels drop.

So highly modified for underwater rock-clinging life that many species are almost unrecognisable as flowering plants at all until they briefly flower during the dry season.

To check whether a plant belongs to Podostemaceae, compare the leaf arrangement, leaf type, flower symmetry, fruit type, and one distinctive marker together. A single feature can mislead; the family pattern is the combination.