Glossary of Fern Terminology



The following Glossary of Fern Terminology was derived from the

Harvard College of Education's website,

FLORADATA. Most definitions have been taken or adapted from

Lellinger, D. B. 2002. A modern multilingual glossary for taxonomic

pteridology. Pteridologia 3. [Washington, D.C.]: American Fern

Society, Inc.).


acroscopic - facing or directed toward the apex of the axis

on which the structure is borne; cf. basiscopic.

acrostichoid - of sori, producing sporangia apparently or

actually spread across the surface of the fertile lamina,

usually densely so.

actinostele (adjective actinostelic) - a radially arranged,

lobed protostele (as seen in cross section) associated with

microphylls, commonly found in the Lycopodiaceae.

aerophore - a spot, swelling, or fingerlike projection of

thin-walled cells found along the stipe or in the pinna or

pinnule axils of some ferns, especially Thelypteridaceae;

more prominent on young fronds.

alate - of spores, with the outer wall (exospore or perispore)

raised in a pattern of narrow, winglike ridges surrounding


alete - of spores, spherical, lacking a laesura, and containing

more sets of chromosomes than normal spores, found

regularly or occasionally in some apomictic ferns.

anadromous - with the basal pinnule and/or vein group of

the pinna directed toward the frond apex; cf. catadromous.

anisophyllous - bearing fronds or microphylls of unequal

size, but of a single shape.

annulus (plural annuli, adjective annular) - a row or patch

of partially or entirely thick-walled cells of the capsule of the

leptosporangium which contracts and forces the capsule to

open and to discharge its spores.

antheridium (adjective antheridial) - the male sex organ

of pteridophytes borne on the gametophyte and producing


apomixis (adjective apomictic) - the formation of a

sporophyte from a gametophyte by direct, asexual

development, rather than by fertilization of gametes.

apophysis (plural apophyses) - a swelling on which a sorus

is located.

archegonium (plural archegonia) - the female sex organ

of pteridophytes borne on the gametophyte and producing


areole (adjective areolate) - an area surrounded by

anastomosing veins.

baculate - of spores, bearing cylindrical projections more

than 1 μm long and less in diam., and usually with an obtuse

to rounded apex.

basiscopic - facing or directed toward the base of the axis

on which the structure is borne; cf. acroscopic.

blade - see lamina

bud - see bulbil

bulbil (adjective bulbiliferous) - a small, usually persistent,

± globose, usually hairy or scaly, asexual propagule borne on

a root, rhizome, or frond and capable or not capable of

forming a plantlet, as in, e.g., certain Asplenium, Bolbitis,

Diplazium, Dryopteris, Huperzia, Polystichum, Tectaria, and

Woodwardia species; synonyms bud, bulblet; see also gemma and


bulblet - see bulbil

capsule - the part of a sporangium that contains the spores.

catadromous - with the basiscopic pinnule and/or vein group of

the pinna the first to depart from its axis; cf. anadromous.

clypeate - shaped like a rounded shield.

coenosorus (plural coenosori) - a compound sorus composed of

several contiguous sori fused end-to-end.

commissure (adjective commissural) - place where a

commissural vein joins parallel, otherwise free veins along the

lamina margin and often underlies a continuous, marginal


costa (plural costae, adjective costal, costate) - the major axis of

a pinna; synonyms midrib, midvein.

costate - of scales, with a central line of cells different (usually

darker) from the more marginal cells, as in certain Aspleniaceae

and Dryopteridaceae; of spores, with the outer wall (exospore or

perispore) raised in a pattern of relatively broad ridges with

rounded crests.

costule (adjective costular, costulate) - the major axis of a

pinnule; synonyms midrib, midvein, rachilla.

crozier - see fiddlehead

ctenitoid - of hairs, with adjacent cells collapsed at right angles

to each other and often the end walls of the cells thickened or

dark-colored, as on some fronds of Ctenitis.

dictyostele (adjective dictyostelic) - a siphonostele with more

than one parenchymatic gap at a single level (as seen in cross


echinate - of spores, with the outer wall (exospore or perispore)

raised in a pattern of long spines.

epispore - a particular, outer, sporopollenin layer of the spore

wall that is external to, but partially attached to, the exospore in

some heterosporous ferns and Equisetum.

exine - see exospore

exospore - the principal sporopollenin layer of the spore wall

internal to the perispore; synonym exine.

false indusium - an introrse, reflexed or revolute, often

modified lamina margin that protects young sporangia.

false vein - an elongate series of thickened cells appearing to be

a vein, but not connected to true veins and not functioning as a

vein; found in the laminae of certain Aspleniaceae,

Hymenophyllaceae, Marattiaceae, Pteridaceae, and


ferns - the pteridophytes excluding the Isoëtaceae,

Lycopodiaceae, and Selaginellaceae.

fiddlehead - the young, unexpanded, circinate apex of a fern

frond; synonym crozier.

frond - the photosynthetic organ of ferns, usually consisting of a

stipe and lamina; synonyms leaf, megaphyll.

gametophyte - an inconspicuous, non-vascular stage in the

life cycle of a pteridophyte that bears gametangia with

gametes. In homosporous pteridophytes, they are either

surficial, thin, chlorophyllous, and various in shape

(filamentous, ribbonlike, heart-shaped, or somewhat stellate)

or subterranean, massive, achlorophyllous, and globose,

cylindrical, or branched. In heterosporous pteridophytes,

they are much reduced structures borne (and partially

developing) within spore walls; synonyms prothallium,


gemma (plural gemmae, adjective gemmiferous) - a

structurally specialized, asexual propagule found on some

gametophytes that detaches and forms a new gametophyte;

also used in the sense of bulbil in some African or European

fern literature.

goniopteroid - of veins, a system of excurrent veinlets

connected to more distal vein unions, or to a translucent line

leading to a sinus, thus forming oblique rhomboid areoles.

hemitelioid - shaped like a shallow saucer or fan, usually

firm and fully or partially surrounding the sorus, typical of

certain Cyatheaceae.

heterosporous (antonym homosporous) - producing

spores of two sizes, each of which develops gametophytes

having gametangia of a single sex.

hydathode - a dark or sometimes pale area of the epidermis

on the adaxial surface of the lamina that coincides with the

endings of the veins and exudes water, salts, etc.

indusium (plural indusia, adjective indusiate) - a usually

thin, often scalelike, epidermal membrane subtending and/or

covering the sorus, that partially or fully protects the young


intrastelar canal - a channel occurring within a stele.

isodromous - with the basal pinnules and/or vein groups of

the pinnae strictly opposite.

isophyllous - having fronds or microphylls of a single size

and shape.

laesura (plural laesurae) - the simple, elongate or triradiate,

scar on the surface of pteridophyte spores; synonym suture.

lamina (plural laminae, adjective laminate) - the expanded

portion of a frond, usually consisting of a rachis or costa,

other axes or lateral veins, and expanded lamina tissue;

synonym blade.

leaf - see frond

leptosporangium (adjective leptosporangiate) - a

thin-walled, thin-pedicelled sporangium bearing usually 64

spores (32 in apomixises of the Dryopteridaceae, 128-512 in

the Osmundaceae, and 256 in the Schizaeaceae) and formed

usually from a single epidermal initial cell.

ligule (adjective ligulate) - a small, tonguelike, often

triangular appendage located near the microphyll base (just

distal to the sporangium on the adaxial surface of the

microsporophyll); it is persistent in Isoëtes.

lophate - of spores, with the outer wall (exospore or

perispore) raised in a pattern of ridges (lophae) surrounding


lumen (plural lumina) - the central cavity of a cell, especially

applied to the cells of clathrate rhizome scales.

lycophytes - collectively the Isoëtaceae, Lycopodiaceae, and


massula (plural massulae) - in Azolla, a structure derived from

the contents of the microsporocarp that contains the microspores

and has glochidia (minute barbed hairs) protruding from its


megagametophyte - in heterosporous pteridophytes, a female

gametophyte borne within a megasporangium and bearing one or

more archegonia.

megaphyll - see frond

megasporangium (plural megasporangia) - a sporangium

bearing megaspores.

megaspore - a large spore of the heterosporous pteridophytes

Azolla, Isoëtes, Marsilea, Pilularia, Regnellidium, Salvinia, and

Selaginella that produces a female gametophyte.

megasporocarp - a sporocarp that bears megasporangia.

megasporophyll - a fertile microphyll bearing or subtending a


microgametophyte - in heterosporous pteridophytes, a male

gametophyte borne within a microsporangium and bearing one or

more antheridia.

microphyll - the photosynthetic organ of the lycophytes,

Equisetaceae, and Psilotaceae, always lacking a stipe, often small

and generally supplied with a single vascular bundle; usually

associated with a protostele or siphonostele.

microsporangium (plural microsporangia) - in heterosporous

pteridophytes, a sporangium bearing microspores.

microsporocarp - a sporocarp that bears microsporangia.

microsporophyll - a fertile microphyll bearing or subtending a


midrib, midvein - see costa, costule, and rachis.

monolete - of spores, bilaterally symmetric with a linear,

unbranched laesura.

murus (plural muri, adjective muriform) - of spores, an

elongate, wall-like protuberance.

paraphysis (plural paraphyses) - a minute, unicellular or

multicellular (resembling a simple hair), usually elongate and

sometimes glandular structure borne on the soral receptacle, on

the sporangium capsule or pedicel.

perine - see perispore

perispore - the outermost, sporopollenin layer of the spore wall

that is deposited on the exospore; synonym perine.

phyllopodium (plural phyllopodia) - in ferns with articulate

stipes, that portion of the stipe proximal to the articulation that

remains attached to the rhizome. Phyllopodia are especially

prominent and stipelike in, e.g., Elaphoglossum and Oleandra but

low and more like the rhizome and knoblike in Adiantum,

Davalliaceae, and many Polypodiaceae.

pinna (plural pinnae, adjective pinnate) - a stalked or sessile,

primary division of a compound lamina that is at least narrowed at

the base.

pinnule - a stalked or sessile division of a pinna that is at least

narrowed at the base.

plectostele (adjective plectostelic) - a vascular cylinder

with the vascular tissue appearing to be ± parallel plates (as

seen in cross section), associated with microphylls, found in

many Lycopodiaceae.

primordium - a part (e.g., a frond) in its most rudimentary

form or stage of development.

proliferous - forming bulbils or plantlets, often on parts

that normally have another function such as roots (e.g.,

Platycerium), stems and branchlets (e.g., Huperzia), rachises

(e.g., most Bolbitis, Diplazium, Dryopteris, some

Hymenophyllaceae, Polystichum, Tectaria, and

Woodwardia) or lamina margin (e.g., some Asplenium).

prothallium, prothallus (plural prothallia, prothalli) - see


protostele (adjective protostelic) - a simple vascular

cylinder that lacks a pith of parenchyma in the center and is

without parenchymatic gaps.

pteridophytes - non-seed-bearing vascular plants; ferns and

lycophytes collectively.

pulvinus (plural pulvini) - a swollen structure at the base of

a frond or at the base of pinnae, particularly common in the


rachilla - see costule.

rachis - the principal, central axis of a pinnatifid or more

compound lamina.

receptacle - the point or region of the lamina tissue, often

thickened and amply supplied by one or more veins, that

produces sporangia and sometimes paraphyses and/or


rhizoid - an elongate, non-vascularized, uni- or

paucicellular structure that serves to anchor the gametophyte

and to absorb water and nutrients from the substrate.

rhizome - in pteridophytes, a scaly or hairy (rarely

glandular or glabrous) anchoring stem that bears roots and


rhizophore - a specialized, aerial root of Selaginella that

arises in the axils of stems and branches repeatedly when in

contact with the substrate; it may occasionally differentiate

into a stem, rather than a root.

rugate - of spores, bearing muri that are wide, rounded, and

non-anastomosing and that do not form areoles.

sinus membrane - an elongate translucent membrane

below the sinus in a pinnule.

siphonostele (adjective siphonostelic) - a vascular cylinder

that has a pith of parenchyma in the center and phloem on

both the outside and inside of the cylinder, or (in the

Osmundaceae) only on the outside of the cylinder.

solenostele (adjective solenostelic) - a siphonostele with

only one parenchymatic gap at a single level (as seen in cross


soriferous - bearing sori.

sorophore - the gelatinous, sporangium-bearing ring

produced by sporocarp (as in the Marsileaceae) during


sorus (plural sori, adjective soral) - a cluster of sporangia.

spermatozoid - a motile male sex cell (gamete) produced

in the antheridium.

sporangiophore - a greatly transformed, peltate sporophyll

bearing a ring of ca. 6 sporangia facing the axis of the strobilus of


sporangium (plural sporangia) - the spore-producing structure

of pteridophytes.

spore - a spherical, tetrahedral, or reniform, often elaborately

ornamented, reproductive cell that is produced within the

sporangium and germinates to form a gametophyte.

sporocarp - in Marsilea, the hard, short- to long-pedunculate,

nutlike structure containing the sporangia, apparently a highly

modified leaflet; in Azolla and Salvinia, a thin, short-stalked,

globose structure containing the sporangia, apparently a modified


sporophore - the fertile portions of a hemidimorphic frond as in

the Ophioglossaceae.

sporophyll - in ferns, a frond bearing sporangia; in the

lycophytes, Equisetaceae, and Psilotaceae, a microphyll

subtending a sporangium; in Isoëtes, an elongate microphyll

bearing a sporangium within its base.

stele (adjective stelic) - the vascular and associated tissues of a

rhizome or other type of stem; see also dictyostele, protostele,

siphonostele, and solenostele.

stipe (adjective stipitate) - the structure of a frond that connects

the base of the lamina to the point of its attachment to the


stipicel - a term sometimes used for the stalk of a pinna or


stipule - in the Marattiaceae, each one of a pair of lateral, fleshy,

starch-bearing, persistent, partially or entirely vascularized

outgrowths of the rhizome that clasp the base of the stipe and that

are capable of vegetatively reproducing the plants; in the

Ophioglossaceae, merely the remnants of the older stipe base that

originally enclosed and protected the younger, less developed


strobilus (plural strobili) - in the lycophytes and Equisetaceae, a

compact reproductive structure borne at the tips of branches or

axes consisting of a central axis bearing closely spaced, spirally

arranged sporophylls or sporangiophores.

suture - see laesura.

synangium (plural synangia) - a group of sporangia partially or

entirely fused laterally, as in Psilotum and Marattiaceae.

trilete - of spores, radially symmetric (spherical or tetrahedral)

with a laesura with three radiating branches.

trophophyll - a vegetative, nutrient-producing frond or


trophopod - the enlarged, persistent, basal portion of a stipe that

functions as a storage organ.

valve - an involucral lobe, especially in Hymenophyllum and

some Dicksoniaceae and Dennstaedtiaceae; also, each half of a

sporangium that is divided into halves, as in the Lycopodiaceae

and Osmundaceae.

vascular bundle - an elongate strand of conducting cells (xylem

tracheids and phloem sieve cells) that serve to conduct water,

mineral nutrients, and photosynthetic products.

velum - in Isoëtes, the membrane covering part or all of the

sporangium-containing cavity (fovea) in the base of a microphyll.



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