Frond
A frond is a large, divided leaf.[1] In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds[2] and some botanists restrict the term to this group.[3] Other botanists allow the term frond to also apply to the large leaves of cycads, as well as palms (Arecaceae) and various other flowering plants, such as mimosa or sumac.[4][5] "Frond" is commonly used to identify a large, compound leaf, but if the term is used botanically to refer to the leaves of ferns and algae it may be applied to smaller and undivided leaves.
Fronds have particular terms describing their components. Like all leaves, fronds usually have a stalk connecting them to the main stem. In
Pinnate fronds
In a frond which is pinnate (feather-shaped), each leafy segment of the blade is called a pinna (plural pinnae), the stalk bearing the pinna is termed a petiolule, and the main vein or mid-rib of the pinna is referred to as a costa (plural costae).[6]
If a frond is divided once into pinnae, the frond is called once pinnate. In some fronds the pinna are further divided into segments, creating a bipinnate frond. The segments into which each pinna are divided are called pinnules, and the extensions of the rachis that support these pinnules, are called rachillae.[7] Rarely, a frond may even be tripinnate, in which case the pinnule divisions are known as ultimate segments.
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).
Non-pinnate fronds
Some fronds are not pinnately compound (or simple), but may be
There is a spectrum from costapalmate to palmate. Costapalmate fronds are shaped like the palm of a hand and have a short midrib or costa. Palmate fronds are also shaped like the palm of the hand, but all ribs or leaflets arise from a central area. A hastula is a flap of tissue borne at the insertion of the blade on the petiole on the upper, lower, or both leaf surfaces[8][9]
Bifurcate fronds may also develop. The extinct
Some ferns, like members of the group
Sporangia
Fern fronds often bear
Fern fronds
Fern fronds, as with all leaves, arise from the stem, either directly, or on an outgrowth from the stem termed a
Fronds may bear hairs, scales, glands, and, in some species, bulblets for vegetative reproduction.
Related concepts
Fronds may describe several "frondose" structures in non-plant organisms -- such as the entire bodies of thalloid organisms, or the superficially leaf-like structures developed by some animals and fungi. Examples include frondose colonial bryozoans,[11] extinct Ediacaran biota such as rangeomorphs,[12] and some macroalgae and lichens.
In paleontology of Ediacaran marine organisms, a frond may be defined as "a rangeomorph unit with a growth tip that can generate primary branches". A frond may also refer to the entire frondose organism, including any stem or basal disc. To classify rangeomorph taxa, the frond is generally subdivided into segments as are those of a fern, and categorized by six factors: polarity, rows of branches, inflation, display/furling, alignment of branches, and presence of a basal disc.[13]
Frondescence is the production of leaves; it can also refer to the abnormal development of floral parts into leafy structures, though this is usually called phyllody.[14]
Cultural significance
The palm frond has been a symbol of victory, triumph, peace, and eternal life originating in the ancient Mediterranean world. For example, in some Christian traditions, during Palm Sunday, Jesus’ entrance into Jerusalem is celebrated by carrying palm leaves.[15]
During the Victorian phenomenon of Pteridomania or "fern craze", fern fronds became wildly popular symbols. Because fronds are somewhat flat, they could be used for decoration in ways that many other plants could not be. They were glued into collectors' albums, affixed to three dimensional objects, used as stencils for "spatter-work", inked and pressed into surfaces for nature printing, and so forth.[16]
The fern flower is a magic flower in Polish folklore.[17] As ferns are non-flowering plants, this technically refers to "fertile fronds". Certain true ferns, e.g., Osmunda regalis have sporangia in tight clusters which may appear flower-like.
See also
- Fern sports – fronds that show marked change from the normal type as a result of mutation
- Acacia filicifolia – a tree whose compound leaves resemble fern fronds
Notes
- ^ Raven, Evert Eichhorn (2004). The Biology of Plants (7th ed.). New York, New York: W.H. Freeman and Company.
- ^ Gifford, Ernest M.; Foster, Adriance S. (1989). Morphology and Evolution of Vascular Plants (3rd ed.). New York, New York: W.H. Freeman and Company.
- ^ Judd, Walter S.; Campbell, Christopher S.; Donoghue, Michael J.; Kellogg, Elizabeth A.; Stevens, Peter F. (2007). Plant Systematics: A Phylogenetic Approach (3rd ed.). Sunderland, Massachusetts: Sinauer.
- ISBN 0730103382.
- ISBN 9780192860941.
- ^ Walters, Keil (1996). Vascular Plant Taxonomy (4th ed.). Dubuque, Iowa: Kendall Hunt Publishing Co.
- ^ "Glossary of Palm Terms | EUNOPS website". eunops.org. Retrieved 2019-12-05.
- ^ "Costapalmate". w3.biosci.utexas.edu. Retrieved 2019-12-05.
- OCLC 890586925.
- PMID 28651518.
- ^ "Cincinnatian Fossils and Stratigraphy". strata.uga.edu. Retrieved 2019-12-05.
- ISSN 0031-0182.
- S2CID 86538017.
- OCLC 29403252.
- ^ "CATHOLIC ENCYCLOPEDIA: Palm in Christian Symbolism". www.newadvent.org. Retrieved 2019-12-05.
- ^ Boyd, Peter. "Pteridomania - the Victorian passion for ferns". www.peterboyd.com. Retrieved 2019-12-05.
- ^ Dworski, Lamus (2016-12-03). "Polish legends: the Fern Flower". Lamus Dworski. Retrieved 2019-12-05.