Different groups of ferns are characterised by their reproductive structures, which can come in many forms. Clockwise from top left: 1) Polystichum; shield ferns. The reproductive structures are aggregated into round patches. Each of the black spheres is a sporangium (plural = sporangia), the capsule that produces the spores (in Polystichum, there are 64 spores in each sporangium). A distinct cluster of sporangia is called a sorus (plural = sori). In many ferns the sori are partially covered by protective tissues, called indusia (singular = indusium). In Polystichum, the indusia are round, giving rise to the common name of shield fern for this group. 2) Cardiomanes; kidney fern. The sori occur on the margins and arise from tubular indusia. 3) Gleichenia; tangle ferns. Two or three sporangia (the yellowish dots) occur on the underside of each frond segment. 4) Hypolepis; pig ferns. The sori are on the margin of the frond and are partially protected by the inrolled margin of the frond. 5) Asplenium; spleenwort ferns. The sori occur in lines away from the margin, and are arranged in a ‘herring bone’ pattern. 6) Pteris. The sori line the margins of the frond. Photos Leon Perrie, montage © Te Papa.