Ferns in Britain and Ireland: Glossary

Glossary

The definitions here given are specific to the plants dealt with in this guide. Some have wider or different meanings in other botanical contexts (capsule, for example).

Abortive	(Of spores): not completely developing and infertile.
Acroscopic	Facing towards the apex (of frond or pinna).
Acute	Angle less than 90°.
Adnate	Attached all along the base, usually applied to a leaf segment.
Alien	Introduced plant that has become established.
Anastomosing	(Of veins): joining up to form a network.
Annulus	The ring or line of thick-walled (indurated) cells on the sporangium that allows it to burst open when ripe (dehisc).
Antheridium; plural: antheridia	Male sex organ, on the underside of the prothallus, that produces sperm.
Apogamous	Ferns that reproduce asexually: the new plants (sporophytes) grow directly from the prothallus, not from a fertilized egg.
Appressed	Lying flat against.
Archegonium; plural: archegonia	The female sex organ containing the egg.
Areole	Area enclosed by netted (anastomosing) veins.
Ascending	Curving upwards.
Attenuate	Gradually tapering to a long thin point.
Auricle	Ear-like lobe at the base of a leaf.
Axil	Angle between the main and side branches.
Axillary	In the axil.
Axis; plural: axes	The primary or central part of of a plant or leaf to which the other parts are joined, eg the rachis or midrib.
Basal cells	Cells in the sporangium, between the annulus and the top of the stalk. The number of these is a diagnostic character in Polypodium.
Basal sinus	Lowest sinus on a leaf.
Basiscopic	Facing towards the base (of frond or pinna).
Bipinnate	Pinnate with the pinnae also pinnate (also 2-pinnate, twice-pinnate); the secondary divisions are called pinnules.
Bipinnate-pinnatifid	As above, but with the pinnules divided again about half to three-quarters of the way to the midrib.
Blade	Main part of the leaf or frond, excluding the stipe.
Bulbil	Small bulb-like or bud-like body borne above the ground on a stem or leaf, which detaches to grow as a new plant - see Huperzia selago. (See also gemma).
Calcicole	A plant that prefers alkaline (base-rich) conditions ("lime-loving").
Calcifuge	A plant that prefers acid (base-poor) conditions ("lime-hating").
Capsule	The part of the sporangium within which the spores develop.
Clathrate	(Of scales): having a latticed appearance under a hand-lens - the result of dark cell walls.
Concolorous	Uniformly coloured.
Cone	Branch tips bearing modified spore-bearing leaves (sporophylls) compressed together so they appear distinct from the other leaves; also known as a strobilus. Found in Horsetails and Clubmosses.
Confluent	Running or merging together.
Contiguous	(Usually of margins of leaf segments): touching each other or running alongside.
Cordate	(Usually of the base of a frond or blade): heart-shaped.
Coriaceous	Leathery in texture.
Costa	Midrib of a pinna.
Crenate	Having rounded teeth.
Crozier	The young leaf forming a coil before it unfurls. (Often called a fiddlehead in the U.S.).
Cuneate	Wedge-shaped.
Cuspidate	Narrowing abruptly to a point.
Decumbent	(Usually of rhizomes): prostrate or flat to the ground but with the tip turned up.
Decurrent	(Of the frond or leaf-segment): having the base extend downwards along the axis.
Dehiscence (verb: to dehisc)	Opening of the sporangium to release the spores.
Dentate	Toothed, with the teeth pointing mostly outwards.
Denticulate	Finely dentate.
Dichotomous	Branching in two.
Dimorphic	Having two forms. Usually applied to fertile and sterile leaves of some ferns, eg Thelypteris, Osmunda.
Diploid	With two matching sets of chromosomes.
Dissected	Deeply divided.
Distal	Furthest away, usually referring to the part of leaf or leaf segment furthest way from the point of attachment.
Distant	Widely spaced, far apart.
Divergent	Growing apart, spreading out.
Dorsiventrally flattened	Flattened to give an upper and a lower surface.
Entire	(Of the margin of leaf): not toothed, lobed or divided.
Ephemeral	Lasting only a short time; (of indusium): quickly shed.
Epiphytic	Growing on trees, using their bark or branches as support but not parasitic on them.
Euphyllophytes	The group containing both ferns (monilophytes) and seed-bearing plants (spermatophytes).
Eutrophic	(Of lakes, ponds, etc.): rich in nutrients.
False indusium	An indusium formed by the rolled-over margin of the leaf enclosing the sorus, as in Adiantum capillus-veneris.
Family	Taxonomical division comprised of a group of related genera.
Fern allies	Group of vascular plants traditionally thought to be closely related to ferns, based mainly on the spore-bearing characteristic. These comprise the families of horsetails (Equisetaceae), quillworts (Isoetaceae), clubmosses (Lycopodiaceae), whisk ferns (Psilotaceae) and spikemosses (Selaginellaceae). Recent research has shown quillworts, clubmosses and spikemosses to be much less closely related to ferns, while horsetails and whisk ferns are more closely related, in fact essentially part of the main fern grouping.
Filiform	Thread-like.
Flabellate	Fan-shaped.
Free	(Of veins): not joined at the ends.
Frond	The leaf of a fern, including the stipe.
Gametophyte	The sexual generation of the fern developing from the spore, generally a small flattish plant (see prothallus). The sex organs (archegonia and antheridia) develop on this, and the fertilization of the egg by the sperm (antherozoid) produces the gamete which develops into the recognizable fern plant (sporophyte).
Gemma; plural: gemmae	A bud or bulbil that detaches from the main plant and develops into a new plant, as in Huperzia selago.
Genus, pl: genera	Taxonomic division comprised of a group of related species.
Glabrous	Hairless and scaleless.
Gland	An organ that secretes a sticky and/or scented juice, usually on the surface of leaf or stem, appearing as a spot, a raised bump or the tip of a hair.
Glandular	Having glands.
Glaucous	Greyish, blue-grey or whitish (often as a bloom on an otherwise green surface).
Globose; globular	Spherical or nearly so.
Haploid	With a single set of chromosomes. This is characteristic of the gametophyte stage.
Heterosporous	With two types of spores: megaspores (female) and microspores (male), as in Isoetes and Selaginella.
Hexaploid	With six sets of chromosomes.
Homosporous	With spores all of a single type, as in most ferns.
Hybrid	Cross between two different taxa. Usually between species, but subspecies may hybridise (see Nothosubspecies), and occasionally hybrids between species belonging to different genera occur.
Imbricate	Overlapping, like roof tiles.
Incised	Cut deeply.
Indurated cells	The thickened cells of the sporangium making up the annulus.
Indusium; plural: indusia	Membrane covering the sorus, not always present, and often shed at some stage in the development of the sorus. See also false indusium.
Internode	The part of the stem between nodes. Used of Equisetum.
Introduced	A plant that was brought into the country (either deliberately or accidently) by man.
Lamina	The leafy part of a frond, not including the midrib, rachis or stipe.
Lanceolate	Lance-shaped: narrow, pointed, slightly wider below the mid-point of the leaf.
Latticed	Forming a mesh.
Leaf	Frond; used here to include both the "leafy" part and the stipe or stem.
Leaf-blade	The "leafy" part of the frond excluding the stipe or stem.
Leaf-segment	Any subdivision of a frond. See pinna, pinnule, pinnulet.
Ligule	Small membrane at the base of the upper side of the leaf, found in Isoetes and Selaginella.
Linear	Long, narrow and parallel-sided or close to.
Lobe	A clear division of a leaf or leaf segment but not so as to be completely cut to the midrib.
Lycophytes	The group comprising quillworts, clubmosses and spikemosses. Distinct from both euphyllophytes, the group that contains both seed plants (spermatophytes) and ferns (monilophytes).
Megasporangium	The sporangium bearing megaspores, in heterosporous plants - Sealaginella and Isoetes.
Megaspore	The female spores, usually relatively large, in heterosporous plants. These give rise to female gametophytes (archegonia).
Micron	One thousandth of a millimetre.
Microsporangium	The sporangium bearing microspores, in heterosporous plants - Sealaginella and Isoetes.
Microspore	The male spores, usually relatively small, in heterosporous plants. These give rise to male gametophytes (antheridia).
Midrib	Central vein of a frond in simple fronds, or of a leaf-segment in divided fronds.
Monilophytes	The group comprising all ferns, now known to include horsetails and whisk-ferns; a recently-coined term to distinguish them from spermatophytes (seed-bearing plants).
Monolete	Having a single rectilinear mark. Used of spores. The mark derives from the way the spore was attached to the other spores in the sporangium. Monolete spores are generally approximately bean-shaped; see also Trilete
Morphotype	An intermediate taxonomic division (not formally recognized), generally used to describe forms at around species level or narrower, where the differentiation is not fully understood (as in Dryopteris affinis).
Mucronate	Terminating abrubtly in a short point.
Native	Occurring naturally, not introduced by man.
Naturalized	An introduced plant that has become established and propogates itself naturally.
Node	The point on a stem where leaves arise. Nodes are most clearly seen in horsetails.
Nothosubspecies, often abbreviated to nothosubsp., nothossp. or n-subsp.	Hybrid where one or both parents is a subspecies (the term nothospecies is occasionally used to denote a hybrid between two species).
Obtuse	Angle greater than 90°.
Oligotrophic	(Of lakes, ponds, etc.): poor in nutrients.
Orbicular	Circular.
Ovate	Egg-shaped (in two dimensions).
Paraphysis; plural: paraphyses	Small hairs, often branched, among sporangia; eg Polypodium cambricum.
Patent	At right-angles.
Peduncle	(Of Clubmosses): the stalk of a cone.
Peltate	Having the stalk attached in the centre.
Persistent	Lasting a long time; (of indusium): remaining in place.
Petiole	The stalk of a leaf; usually referred to as a stipe in ferns.
Pinna; plural: pinnae	Primary division of a leaf. Pinnae are attached to the rachis by their midribs.
Pinna segment	Division of a pinna, whether cut entirely to the midrib or not.
Pinnate	Having the leaf divided once into distinct leaflets; like a double-sided comb (also 1-pinnate, once-pinnate). 2-pinnate = having the primary divisions are themselves pinnate (also bipinnate, twice-pinnate).
Pinnate-pinnatifid	Pinnate, with the pinnatifid pinnae (divided, but not all the way to the midrib).
Pinnatifid	Having the leaf divided once into distinct divisions, but not cut all the way to the rachis, so not forming separate leaflets.
Pinnatisect	As pinnatifid but cut almost all the way to the rachis.
Pinnule	Secondary division of a leaf. Pinnules are disions of pinnae.
Pinnule segment	Division of a pinnule, whether cut entirely to the midrib or not.
Pinnulet	Tertiary division of a leaf. Pinnulets are divisions of pinnules.
Polyploid	With more than two sets of chromosomes.
Procumbent	Lying flat along the ground.
Prothallus	The gametophyte stage of the fern. This is the independent stage where sexual reproduction takes place. In most ferns, it is a small, flattish, often roughly heart-shaped body.
Proximal	Closest, usually referring to the part of leaf or leaf segment closest to the point of attachment.
Pteridophyte	Traditional term encompassing both ferns and "fern allies"; the latter now known to be composed of some groups which are essentially ferns but look unlike them, and others which are not at all closely related. See Lycophytes, Monilophytes, Euphyllopytes.
Pubescent	Covered in small fine hairs.
Rachis (also rhachis); plural: rachides or rachises	The section of midrib within the leafy part of the frond, ie above the stipe.
Receptacle	The part of the frond to which the sorus is attached; often raised slightly above the surface.
Reflexed	Bent backwards or downwards.
Reniform	Kidney-shaped.
Reticulate	(Usually of veins): forming a network.
Rhachis	See rachis
Rhizome	Stem of the fern plant, as opposed to the stem of an individual leaf which is called a stipe. In ferns, this is is often partially hidden, indistinct or partially underground. It may be creeping, as in Polypodium, or upright and highly visible as in tree-ferns.
Rugose	Wrinkled.
Scale	Small, often semi-transparent outgrowth of the outer layer of cells (epidermis). Usually most frequent towards the lower part of the stipe. Must be at least two cells wide to qualify as a scale - if only one cell wide it's a hair. Dicksonia species, for example, have hairs instead of scales.
Scarious	Thin, dry-looking, translucent, often whitish.
Sessile	Unstalked.
Simple	Not divided. Applies to a whole leaf, as opposed to entire.
Sinus	The gap or indentation between teeth or lobes of frond.
Sorus	A cluster of sporangia.
Species	Taxonomic division generally used to describe those plants that will interbreed freely with each other and share a range of visual similarities. There is, however, no precise, universally agreed definition.
Spermatophytes	Seed-bearing plants.
Spinose	With spines.
Spinulose	With small spines.
Sporangium; plural: sporangia	The spore case; capsule containing spores. A group of sporangia make up a sorus.
Spore	The minute, single-celled body which develops in the sporangium. When released it germinates and develops into the gametophyte.
Sporeling	Tiny fern plant still attached to the gametophyte from which it has developed.
Sporocarp	A globose structure that contains the sporangia in Pilularia.
Sporophyll	Fertile leaf that carries the sporangia in clubmosses.
Sporophyte	The generation of the fern that produces the spores. This is the main visible plant that is normally thought of as the actual fern. See gametophyte.
Stipe	Stalk of the leaf, ie the part of the midrib below the leafy part or blade.
Stolon	Runner from the main stem, producing a new plant that roots independently.
Strobilus; plural: strobili	The cone. Branch tips bearing modified spore-bearing leaves (sporophylls) compressed together so they appear distinct from the other leaves. Found in Horsetails and Clubmosses.
Subspecies, often abbreviated to spp. or subsp.	Subdivision of a species.
Taxon; plural: taxa	Any members of a specific taxonomic grouping, eg species, genus, etc. So one may refer to the Asplenium trichomanes and Asplenium ruta-muraria taxa (species); Dryopteris and Polystichum taxa (genus); or the Lycopodiacae and Selaginellaceae taxa (family).
Terminal	At the tip.
Terrestrial	Growing on the ground.
Tetraploid	With four matching sets of chromosomes.
Tooth	Small lobe.
Transverse	At right angles; cross-ways.
Trilete	Having a distinct Y-shaped mark. Used of spores. The mark derives from the way the spore was attached to the other spores in the sporangium; see also Monolete
Tripinnate	Pinnate with the pinnae and pinnules also pinnate (also 3-pinnate, thrice-pinnate).
Triploid	With three matching sets of chromosomes.
Ultimate segment	The final, smallest divisions of a leaf.
Variety, often abbreviated to var.	Subdivision of species, but less well-defined that a subspecies.
Vein	Strands of vascular tissue, normally visible in leaves.
Venation	The pattern formed by the veins in the leaf.
Verrucose	Covered in small warts.