For the album by Pond, see Frond (album). For animals and fossils with frondlike structures, see Frondose.
The names of fern frond parts (Davallia tyermannii)A fern (Dryopteris decipiens) with simple (lobed or pinnatifid) blades, the dissection of each blade not quite reaching to the rachis.A growing fern frond unfurling.Unfurling fiddlehead fern 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 botany, this leaf stalk is generally called a petiole, but in regard to fronds specifically it is called a stipe, and it supports a flattened blade (which may be called a lamina), and the continuation of the stipe into this portion is called the rachis. The blades may be simple (undivided), pinnatifid (deeply incised, but not truly compound), pinnate (compound with the leaflets arranged along a rachis to resemble a feather), or further compound (subdivided). If compound, a frond may be compound once, twice, or more.
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 palmate, costapalmate, or bifurcate.
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 Devonianseed plantCosmosperma polyloba demonstrated the early evolutionary diversification of frond branching patterns, presenting both bifurcate and trifurcate types.[10]
Some ferns, like members of the group Ophioglossales have a unique arrangement -- such as a single fleshy or amorphous leaf.
Adaxial (left) and abaxial (right) surfaces of a pinnate fern frond (Blechnum appendiculatum). Sori are evident on the abaxial surface.
Sporangia
Fern fronds often bear sporangia, where the plant's spores are formed, usually on the underside (abaxial surface) of the pinnae, but sometimes marginally or scattered over the frond. The sporangia are typically clustered into a sorus (pl., sori). Associated with each sorus in many species is a membranous protective structure called an indusium, which is an outgrowth of the blade surface that may partly cover the sporangia. Some fern species feature frond dimorphism, in which fertile and sterile fronds differ in appearance and structure.
Fern fronds
Fern fronds, as with all leaves, arise from the stem, either directly, or on an outgrowth from the stem termed a phyllopodium. The stem of a typical (leptosporangiate) fern is subterranean or horizontal on the surface of the ground. These stems are called rhizomes. Many fern fronds are initially coiled into a fiddle-head or crozier (see circinate vernation), although cycad and palm fronds do not have this pattern of new leaf growth.
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]
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
↑ Raven, Evert Eichhorn (2004). The Biology of Plants (7thed.). New York, New York: W.H. Freeman and Company.
↑ Gifford, Ernest M.; Foster, Adriance S. (1989). Morphology and Evolution of Vascular Plants (3rded.). 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 (3rded.). Sunderland, Massachusetts: Sinauer.
↑ Jones, David L. (1993). Cycads of the World. Smithsonian Institution Press, USA. ISBN0730103382.
↑ Burzynski, Greg; Narbonne, Guy M. (2015-09-15). "The discs of Avalon: Relating discoid fossils to frondose organisms in the Ediacaran of Newfoundland, Canada". Palaeogeography, Palaeoclimatology, Palaeoecology. Ediacaran Environments and Ecosystems. 434: 34–45. Bibcode:2015PPP...434...34B. doi:10.1016/j.palaeo.2015.01.014. ISSN0031-0182.
Pinnation is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in patterns of erosion or stream beds.
Asplenium platyneuron, commonly known as ebony spleenwort or brownstem spleenwort, is a fern native to North America east of the Rocky Mountains. It takes its common name from its dark, reddish-brown, glossy stipe and rachis, which support a once-divided, pinnate leaf. The fertile fronds, which die off in the winter, are darker green and stand upright, while the sterile fronds are evergreen and lie flat on the ground. An auricle at the base of each pinna points towards the tip of the frond. The dimorphic fronds and alternate, rather than opposite, pinnae distinguish it from the similar black-stemmed spleenwort.
A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls bear either megasporangia and thus are called megasporophylls, or microsporangia and are called microsporophylls. The overlap of the prefixes and roots makes these terms a particularly confusing subset of botanical nomenclature.
Myriopteris gracillima, formerly known as Cheilanthes gracillima, is a species of lip fern known by the common name lace lip fern. It is native to western North America, where it grows in rocky habitat from British Columbia to California to Montana.
Dryopteris intermedia, the intermediate wood fern or evergreen wood fern, is a perennial, evergreen wood fern native to eastern North America. It is a diploid species, and is the parent of several species of hybrid origin, including Dryopteris carthusiana. Other common names for this species include intermediate shield fern, fancy wood fern, fancy fern, glandular wood fern, American shield fern and common wood fern.
The Lyginopteridales are an extinct group of seed plants known from the Paleozoic. They were the first plant fossils to be described as pteridosperms and, thus, the group on which the concept of pteridosperms was first developed; they are the stratigraphically oldest-known pteridosperms, occurring first in late Devonian strata; and they have the most primitive features, most notably in the structure of their ovules. They probably evolved from a group of Late Devonian progymnosperms known as the Aneurophytales, which had large, compound frond-like leaves. The Lyginopteridales became the most abundant group of pteridosperms during Mississippian times, and included both trees and smaller plants. During early and most of middle Pennsylvanian times the Medullosales took over as the more important of the larger pteridosperms but the Lyginopteridales continued to flourish as climbing (lianescent) and scrambling plants. However, later in Middle Pennsylvanian times the Lyginopteridales went into serious decline, probably being out-competed by the Callistophytales that occupied similar ecological niches but had more sophisticated reproductive strategies. A few species continued into Late Pennsylvanian times, and in Cathaysia and east equatorial Gondwana they persisted into the Late Permian, but subsequently became extinct. Most evidence of the Lyginopteridales suggests that they grew in tropical latitudes of the time, in North America, Europe and China.
Asplenium bradleyi, commonly known as Bradley's spleenwort or cliff spleenwort, is a rare epipetric fern of east-central North America. Named after Professor Frank Howe Bradley, who first collected it in Tennessee, it may be found infrequently throughout much of the Appalachian Mountains, the Ozarks, and the Ouachita Mountains, growing in small crevices on exposed sandstone cliffs. The species originated as a hybrid between mountain spleenwort and ebony spleenwort ; A. bradleyi originated when that sterile diploid hybrid underwent chromosome doubling to become a fertile tetraploid, a phenomenon known as allopolyploidy. Studies indicate that the present population of Bradley's spleenwort arose from several independent doublings of sterile diploid hybrids. A. bradleyi can also form sterile hybrids with several other spleenworts.
Diplazium australe, commonly known as the Austral lady fern, is a small fern occurring in eastern Australia, New Zealand and Norfolk Island. The habitat is moist shaded areas, often occurring in rainforest.
Adiantum viridimontanum, commonly known as Green Mountain maidenhair fern, is a fern found only in outcrops of serpentine rock in New England and Eastern Canada. The leaf blade is cut into finger-like segments, themselves once-divided, which are borne on the outer side of a curved, dark, glossy rachis. These finger-like segments are not individual leaves, but parts of a single compound leaf. The "fingers" may be drooping or erect, depending on whether the individual fern grows in shade or sunlight. Spores are borne under false indusia at the edge of the subdivisions of the leaf, a characteristic unique to the genus Adiantum.
Pseudopedate is a term used in botany to describe the leaf architecture of certain ferns in the genus Adiantum.
Acacia filicifolia, commonly known as fern-leaved wattle, is a plant in the legume family, Fabaceae and is native to eastern Australia. It is a shrub or tree with compound leaves resembling fern fronds, and spherical heads of yellow or bright yellow flowers from autumn to late spring. It is a common and widespread species, especially on the coast and tablelands of New South Wales.
Gleichenia alpina, commonly known as alpine coral-fern, is a small fern species that occurs in Tasmania and New Zealand. It grows in alpine and subalpine areas with moist soils and is a part of the Gleichrniaceae family.
Asplenium × wherryi, known as Wherry's spleenwort, is a rare hybrid fern of the Appalachian Mountains. The sterile triploid offspring of mountain spleenwort (A. montanum) and Bradley's spleenwort (A. bradleyi), it is known from a few sites where those species grow together. First collected by Edgar T. Wherry in 1935, it was largely ignored until a new colony was found in 1961, and the species was named in his honor.
Asterotheca is a genus of seedless, spore-bearing, vascularized ferns dating from the Carboniferous of the Paleozoic to the Triassic of the Mesozoic.
Myriopteris tomentosa, formerly known as Cheilanthes tomentosa, is a perennial fern known as woolly lipfern. Woolly lipfern is native to the southern United States, from Virginia to Arizona and Georgia, and Mexico.
Frondosity is the property of an organism that normally flourishes with fronds or leaf-like structures.
Myriopteris maxoniana is a species of cheilanthoid fern known only from one collection in Tamaulipas, Mexico. It closely resembles Myriopteris longipila and was not described as a distinct taxon until 2004.
Myriopteris aemula, the Texas lip fern or rival lip fern, is a moderately-sized fern of Texas and Mexico, a member of the family Pteridaceae. Unlike many members of its genus, its leaves have a few hairs on upper and lower surfaces, or lack them entirely. One of the cheilanthoid ferns, it was usually classified in the genus Cheilanthes as Cheilanthes aemula until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on limestone rock.
Argyrochosma connectens is a small cheilanthoid fern endemic to Sichuan, China. It is the only member of its genus known from Asia. Relatively rare, it is found growing in the crevices of limestone rocks in hot, dry valleys. The species was long classified in the genus Pellaea, but after a phylogenetic study in 2015 was transferred to Argyrochosma.
Argyrochosma palmeri is a fern endemic to Mexico. It has narrow, divided leaves with black axes; the leaves are coated in white powder below, and sparsely dusted or free of it above. First described as a species in 1887, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".
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