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NZ Plants


Fertile and sterile fronds

In some ferns sporangia are restricted to special fronds with a distinctive form while in other ferns sporangia are restricted to special leaflets in a specific location.

Fertile and sterile fronds of different form on the same plant


During every growing season, some adult ferns form:
-- sterile fronds that lack sporangia
-- fertile fronds that bear sporangia
The two types of fronds often differ in appearance, a condition known as frond dimorphism (di, two; morph, form). Frond dimorphism is found in many genera of New Zealand ferns.

Plant with erect fertile fronds and prostrate sterile fronds
(photo, L Jensen)

Blechnum procerum- A plant with prostrate sterile fronds and erect fertile fronds. 

More on this group of ferns

Fertile frond (left) and sterile frond (right)
(photo, I MacDonald)

Blechnum procerum- Fertile frond (left) and sterile frond (right) 

Fertile and sterile leaflets of different form on the same plant

In some ferns all the fronds have a similar appearance but only some pinnae are fertile, eg. the sporangia are restricted to specific locations on the frond.

Fertile frond upper surface, basal portion with fertile secondary leaflets
(photo, L Jensen)


Todea barbara - Basal portion of a frond, upper surface. Only the basal pairs of secondary leaflets bear sporangia. These often differ in size from the adjacent sterile leaflets.

More on this fern 

Fertile frond lower surface, basal portion with fertile secondary leaflets
(photo, L Jensen)

Todea barbara - Basal portion of a frond, lower surface. Sporangia are resricted to the fertile secondary leaflets.