Vernation or leafing[.] is the formation of new leaf or . In plant anatomy, it is the arrangement of leaves in a bud.
In pine species, new leaves are short and encased in Leaf sheath. Each leaf bundle consists of two to five needles. All the leaves on one section of branch grow in length together. In cabbage species, new leaves are folded over, each covered by the previous leaf.
Name
The term
vernation is borrowed from
New Latin , the act of being verdant or flourishing (vernare]]). It is cognate with (
Latin language for "spring") and ("vernal").
Circinate vernation
Circinate vernation 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
Photosynthesis, 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
The process of
convolute vernation involves the wrapping of one margin of the leaf's blade over the other. This folding mechanism makes the emerging leaf look like a tube.
Involute vernation
In
involute vernation both margins on opposing sides of the leaf are rolled up towards the upper (axial) surface of the leaf, forming two tubes that may meet at the
midrib of the leaf.
Revolute vernation
Revolute vernation is the opposite of involute vernation: the margins of the leaf are rolled up towards the under (abaxial) surface of the leaf.
See also
-
Aestivation — the way in which the and of a flower are arranged in a bud.
-
— the way an individual leaf is folded within a bud.
