Everything about Frond totally explained
A
frond is a large
leaf with many divisions to it, and the term is typically used for the leaves of
palms,
ferns or
cycads.
A frond is the
leaf- like structure of a
fern or
alga. The term is colloquially applied to the leaves of
palms,
cycads, and plants with pinnately compound leaves. A significant difference is that, unlike the leaves of the latter, fern fronds bear the reproductive structures (spore-bearing structures) of the sporophyte plant. Because many ferns grow fronds that are held more vertical than horizontal, the "upper" and "lower" surfaces of a frond are more correctly referred to as the
adaxial and
abaxial surfaces, respectively.
A fern frond consists of a
stipe, the stem supporting the
blade, and the blade consists of both a laminar (flattened) photosynthetic tissue and a
rachis—that portion of the stem to which the laminar tissue is attached. The blades of fern fronds may vary from being simple (undivided) to being highly dissected, even "lace-like". If the leaf tissue is undissected, or the dissections don't reach to the
rachis, the frond may be described as lobed or
pinnatifid. Otherwise, the blade is compound and each large division of the laminar tissue arising from the rachis is called a
pinna (pl.,
pinnae). The main vein or mid-rib of a pinna is known as a
costa (pl.,
costae). Pinnae may be arranged along the
rachis either directly opposite one another or alternating up the stem. The arrangement may change from the base of a blade to the tip, as in the example of
Blechnum shown below (from base to tip: pinnae opposite to alternate, and pinnatisect to pinnatifid).
Many ferns have
pinnae that are divided two or more times, and the level of division of the fronds is termed
pinnate (or 1-pinnate), or
twice-pinnate (2-pinnate), or the like. Each secondary division (division of a pinna) is termed a
pinnule, and its mid-vein, a
costule. A few species of ferns with divided fronds are not
pinnate, but are
palmate or
bifurcate.
On some or all mature blades (usually on the
abaxial surface) occur
sporangia, which bear the
spores. The sporangia are clustered in a
sorus (pl.,
sori) or "fruit dot". Associated with each sporus in many species is a membranous structure called an
indusium: an outgrowth of the blade surface that may partly cover the sporangial cluster. Fronds also may bear hairs or scales, glands, and, in some species, bulblets for vegetative reproduction.
Each frond arises from the stem or
rhizome, which in most species is concealed in the ground or creeps along the ground (or branch or rock) surface. Growth of a fern frond differs from that of a leaf of a
flowering plant. The fern frond unrolls from a tightly-coiled structure called a "fiddle-head" (see
circinate vernation).
Some fern species feature
frond dimorphism, in which fertile and sterile fronds differ in appearance and structure.
Footnote
Further Information
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