Vernation (from ''vernal'' meaning ''spring'', since that is when leaves spring forth in
temperate regions) is the formation of new
leaves
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
or
frond
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
s. In plant anatomy, it is the arrangement of leaves in a
bud
In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
.
In
pine species, new leaves are short and encased in
sheath
Sheath pronounced as , may refer to:
* Scabbard, a sheath for holding a sword, knife, or other large blade, as well as guns, such as rifles.
* The outer covering of a cable
* Condom, a kind of contraception
* Debye sheath, a layer of a plasma ...
s. Each leaf bundle consists of 2 to 5 needles. All the leaves on one section of branch grow in length together. In
cabbage
Cabbage, comprising several cultivars of ''Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.&nbs ...
species, new leaves are folded over, each covered by the previous leaf.
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
A crosier or crozier (also known as a paterissa, pastoral staff, or bishop's staff) is a stylized staff that is a symbol of the governing office of a bishop or abbot and is carried by high-ranking prelates of Roman Catholic, Eastern Cathol ...
'' (after the
shepherd's crook) or ''
fiddlehead
Fiddleheads or fiddlehead greens are the furled fronds of a young fern, harvested for use as a vegetable.
Left on the plant, each fiddlehead would unroll into a new frond (circinate vernation). As fiddleheads are harvested early in the sea ...
'' (after the
scrollwork
The scroll in art is an element of ornament and graphic design featuring spirals and rolling incomplete circle motifs, some of which resemble the edge-on view of a book or document in scroll form, though many types are plant-scrolls, which l ...
at the top of a violin). As the lower parts of the frond expand and toughen up, they begin to
photosynthesize
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
, 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
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
of
cycads
Cycads are seed plants that typically have a stout and woody ( ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...
. Circinate vernation is also typical of the carnivorous plant family
Droseraceae,
for example see
this photo of ''
Drosera filiformis
''Drosera filiformis'', commonly known as the thread-leaved sundew, is a small, insectivorous, rosette-forming species of perennial herb. A species of sundew, it is unusual within its genus in that the long, erect, filiform (thread-like) leave ...
''. It is also seen in the related genera ''
Drosophyllum'' and ''
Triphyophyllum
''Triphyophyllum'' is a monotypic plant genus, containing the single species ''Triphyophyllum peltatum'' of the family Dioncophyllaceae. It is native to tropical western Africa, in Ivory Coast, Sierra Leone and Liberia, growing in tropical ...
'', and in the much more distantly related ''
Byblis
In Greek mythology, Byblis or Bublis (Ancient Greek: Βυβλίς) was a daughter of Miletus. Her mother was either Tragasia, daughter of Celaenus; Parthenius, ''Erotica Pathemata'' 11 Cyanee, daughter of the river-god Meander, or Eidothea, ...
''; 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
This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...
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
Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a ...
— the way in which the
petals and
sepals of a flower are arranged in a bud.
*
Ptyxis — the way an individual leaf is folded within a bud.
References
{{NSRW Poster
Plant morphology
