Circinate vernation (or
circinnate, from Latin "made round") is the manner in which most
fern fronds emerge. As the fern frond is formed, it is tightly curled so that the tender growing tip of the frond (and each subdivision of the frond) is protected within a coil. At this stage it is called a
crozier (after the
shepherd's crook) or
fiddlehead (after the
scrollwork at the top of a violin). As the lower parts of the frond expand and toughen up, they begin to
photosynthesize, supporting the further growth and expansion of the frond. By photosynthesizing, the frond increases the amount of solute inside the frond, which lowers the internal water gradient and facilitates an increase in volume that forces uncoiling. In the case of many fronds, long hairs or scales provide additional protection to the growing tips before they are fully uncoiled. Circinate vernation may also be observed in the extension of
leaflets, in the
compound leaves of
cycads. Circinate vernation is also typical of the carnivorous plant family
Droseraceae, for example see
this photo of
Drosera filiformis. It is also seen in the related genera
Drosophyllum and
Triphyophyllum, and in the much more distantly related
Byblis; however in these three genera, the leaves are coiled
outwards towards the abaxial surface of the leaf (reverse circinate vernation): this appears to be unique to these three plants among the angiosperms. ==Convolute vernation==