British ferns (Filicopsida)

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L. Watson and M. J. Dallwitz

Character List

#1. <Common name:>/

#2. <Synonyms:>/

Sporophyte

#3. Plants <whether rhizomatous>/

1. rhizomatous /

2. not rhizomatous/

#4. The rhizomes <slender or stout>/

1. slender/

2. stout/

#5. The rhizomes <orientation>/

1. creeping/

2. ascending/

3. erect/

#6. The rhizomes <hairy or scaly> /

1. hairy /

2. bearing scales /

3. naked <with neither hairs nor scales> /

#7. The <erect> rhizomes <whether becoming trunk-like>/

1. becoming trunk-like beneath the crown of leaves, potentially to several meters high, covered with the blackened, persistent petiole bases and matted on the lower part with fibrous roots <tree ferns>/

2. not becoming trunk-like as in tree ferns /

#8. Plants <whether sterile and fertile leaves differ in form>/

1. bearing markedly different fertile and sterile leaves/

2. with no clear distinction into fertile and sterile leaves <i.e., apart from presence or absence on them of sporangia> /

#9. Plants <very peculiar forms: Ophioglossaceae, Marsileaceae> /

1. usually bearing only a single leaf comprising two pinnae, the lower leaf-like, the upper fertile and non-laminate <Ophioglossaceae> /

2. resembling duckweed - floating, with pendulous roots and tiny leaves <Azolla> /

3. rooted, helophytic or aquatic, with subulate leaves <Pilularia> /

4. conventionally fern-like in form /

#10. Plants <key features for Ophioglossum spp.>/

1. having sterile blades mostly 3–3.5 cm long, the sporangia 6–14 on either side of the spike/

2. having sterile blades mostly 4–15 cm long, the sporangia 10–40 on either side of the spike/

#11. Leaves <living, whether aggregated in terminal tufts>/

1. distributed along the rhizomes <not aggregated terminally>/

2. aggregated terminally <at the crown, or on main branches of the rhizome>/

The variations in growth form to which this alludes are often mentioned in published descriptions and evidently have potential value for identification, but there is a need for reliable comparative observations in terms of better character and state definitions.

#12. Leaves <whether rooting from their tips>/

1. rooting at their tips from a scaly bud <Woodwardia radicans>/

2. not rooting at their tips /

#13. Leaves to <maximum length, including petiole>/

cm long/

#14. Leaves <longevity>/

1. persistent <through the winter>/

2. dying in the autumn/

A feature quite widely mentioned in published descriptions, and potentially a very useful character in keys, for which confirmatory observations and more data are needed.

#15. Leaves <vernation, whether circinnate>/

1. circinnate /

2. not circinnate/

Circinnate (circinate): of a leaf which develops in a coil, with the apex at its centre. Characteristic of most ferns and cycads, but unusual in angiosperms.

#16. <Vernation details, distinguishing Gymnocarpium spp.:>/

1. the two unfolded basal pinnae and the rest of the blade rolled separately into three small ‘balls’ in the young leaf/

2. the unfolded leaf with each pinnule and pinna rolled separately, all enclosed in one ‘ball’/

Pinna: a primary branch of a compound leaf.

#17. Leaves <form>/

1. subulate/

2. laminate /

#18. Leaves <simple or compound> /

1. simple /

2. compound /

Compound here denotes leaves with distinct pinnae or orders of pinnae, the pinnae being stalked (rachillate) or with much narrowed bases on a non-laminate main axis (rachis). Note that simple leaves may be variously lobed or dissected. For example, the pinnately compound leaf of Blechnum (q.v.) is to be distinguished from the simple, pinnately lobed (dissected) one of Polypodium (q.v.).

In attempting to identify ferns, it is essential to avoid confusing the stem-like petioles and pinnae of complexly compound leaves with stems. If necessary, examine a plant of bracken to confirm that you understand its structure in this context.

#19. Leaves <simple, whether entire or lobed>/

1. entire/

2. somewhat lobed/

3. conspicuously, pinnately lobed/

4. more or less dichotomously divided and 1–2(-3) times forked, the stalked forks often unequal, the segments linear-cuneiform/

#20. Leaves <compound, whether simply or complexly divided>/

1. simply divided <once pinnate with undivided or merely crenate pinnae>/

2. complexly divided <with two or more orders of deep dissection, regardless of whether this involves lobing or compounding>/

In complexly divided fern leaves, the degree of complexity decreases towards the apex.

In attempting to identify ferns, it is essential to avoid confusing the stem-like petioles and pinnae of complexly compound leaves with stems. If necessary, examine a plant of bracken to confirm that you understand its structure in this context.

Pinna: a primary (first order) branch of a compound leaf, usually but not always laminate.

Pinnule: a subdivision of a pinna of a bipinnate leaf, or an ultimate unit of a complexly compound one (usually but not always laminate).

#21. Leaves <compound and complexly divided, detailed form>/

1. once pinnate, with conspicuously divided pinnae/

2. bipinnate with more or less undivided pinnules/

3. bipinnate with conspicuously divided pinnules/

4. tripinnate with undivided ultimate pinnules/

5. tripinnate with conspicuously divided ultimate pinnules/

6. 4-pinnate/

#22. The lower pinnae <shape and carriage: Pteridium>/

1. linear-lanceolate with drooping tips/

2. broadly ovate with upwardly curving tips/

#23. <Primary> pinnae <number on each side of the leaf>/

<first order> on each side of the leaf/

#24. Leaves <whether bent at the rachis/petiole junction>/

1. conspicuously bent near the junction of rachis and petiole <Phegopteris, Gymnocarpium, etc.>/

2. not conspicuously bent near the junction of rachis and petiole <i.e., straight or curved> /

#25. The leaves <whether Pteris type>/

1. compound-pinnate, with long, narrow pinnae of which only the lowest on each side bears a single pinnule/

2. not as in Pteris (q.v.) /

#26. The fertile leaves <specialisation of form> /

1. having the appearance of a stem with a terminal fertile portion and a single lateral leaf, but actually comprising two pinnae, the upper fertile, stalked and non-laminate, the lower sterile, sessile, and laminate <Ophioglossaceae> /

2. bipinnate with several pinnae, the lower (proximal) pinnae bearing normal green pinnules, but those of the upper (distal) pinnae non-laminate, more or less linear, and densely covered with sporangia <Osmundaceae> /

#27. The sterile green blades <of Ophioglossum species: length>/

cm long/

#28. The sterile green blades <form>/

1. pinnate/

2. simple and entire/

#29. The green blades <venation: distinguishing Ophioglossum spp.>/

1. with free vein endings within the network/

2. without free vein endings within the network/

#30. The fertile spikes <of Ophioglossum species: length>/

cm long/

#31. The fertile spikes <Ophioglossum/Botrychium: whether branched>/

1. branched/

2. unbranched/

#32. The petioles <length relative to that of the blades>/

1. shorter than the blades/

2. about as long as the blades/

3. longer than the blades/

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

#33. The petioles about <detailed length relative to the blade>/

x the length of the blade/

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

#34. The petioles <stipe: whether jointed>/

1. jointed and ultimately abscising at the point of attachment to the rhizome/

2. jointed and ultimately abscising in the mid-region/

3. not jointed <without a clear abscission zone> /

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

#35. The petioles <stipe: vascularization (see 'Notes')>/

1. vascularised via a single strand/

2. vascularised by several discrete strands/

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

The extensive variations in vascular patterns exhibited by fern leaves (cf. De Bary, 1884) have obvious taxonomic potential, but there is a need for competent comparative studies. Since descriptions in floras generally give no information on the positions at which petiolar sections are to be made, the compiled data are almost useless.

#36. Petiolar scales <colour and density>/

1. golden brown and often dark centred, dense <Drypoteris remota>/

2. not golden brown/

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

#37. <Colour and form of petiole and rachis (Asplenium spp.)> /

1. the petioles and rachides blackish, both with very narrow brownish wings <A. trichomanes> /

2. the petioles brownish or blackish only near the base and green above, the rachides green and either wingless or at most only narrowly green-winged <A. viride> /

Petiole: the component of a leaf joining the stem (usually a rhizome) and proximal to the lowest pinna or (in a simple leaf) to the lamina. The leaf stalk, or stipe.

Rachis: the main axis of a compound leaf above the lowest pinna. Not to be confused with the petiole (q.v.), which is the component joining the rhizome and proximal to the lowest pinna or (in a simple leaf) to the lamina.

#38. Leaf blades in outline <shape>/

1. linear/

2. oblong/

3. elliptic/

4. ovate/

5. ovate-triangular <deltoid>/

6. lanceolate/

7. lanceolate-triangular/

8. oblanceolate/

This aims to describe the outline of the laminate part of the leaf, regardless of the degree of dissection.

#39. Leaf blades <translucence>/

1. very thin and translucent - only one cell thick, lacking stomata/

2. not thin and translucent /

#40. Leaf blades <whether leathery>/

1. leathery/

2. ‘herbaceous’ <not leathery> /

#41. Leaf blades <whether lemon-scented>/

1. faintly lemon-scented when crushed <Oreopteris>/

2. not lemon-scented when crushed /

#42. Leaf blades <abaxial covering of reddish brown scales>/

1. covered underneath with rust-coloured scales <Ceterach>/

2. not covered underneath with rust-coloured scales /

#43. The lowermost pair of pinnae <whether bent backwards>/

1. rather conspicously bent backwards away from the rest <Phegopteris>/

2. not conspicuously bent backwards away from the rest/

Pinna: a primary (first order) branch of a compound leaf.

#44. The longest <primary> pinnae <location along the leaf blade>/

1. the lowermost/

2. near the base of the blade/

3. about a third of the distance from the base of the blade/

4. around the middle of the blade/

5. above the middle of the blade/

Pinna: a primary (first order) branch of a compound leaf.

#45. The longest <primary> pinnae <length>/

cm long/

Pinna: a primary (first order) branch of a compound leaf.

#46. The <primary> pinnae <relative lengths along the blade> /

1. decreasing markedly in length towards the base of the blade, the basal ones relatively short /

2. not decreasing markedly in length basipetaly, the basal pinnae not or scarcely shorter than the longest pair /

#47. The bases of the pinnae <presence of basal dark blotch>/

1. with a dark brown or blackish blotch above, at the junction with the rachis/

2. without a dark blotch at the base/

Rachis: in this context, the main axis of a compound leaf above the lowest pinna. Not to be confused with the petiole (q.v.), which is the component joining the rhizome and proximal to the lowest pinna or (in a simple leaf) to the lamina.

Pinna: a primary (first order) branch of a compound leaf.

#48. The lowest pinna <relative lengths of lowest pinnules>/

1. with the lowest 3 or 4 pinnules on either side all about equal in length/

2. with the lowest pinnule on the lower side much longer than the lowest one on the upper side, and often longer than the one or two adjoining it as well/

#49. The lowest pinna <relative length of its basal pinnule on the lower side>/

1. with the basal pinnule on its lower side generally at least half as long as the pinna itself/

2. with the basal pinnule on its lower side nearly always less than half as long as the pinna itself/

#50. The adjacent pinnae <adjacent or separated>/

1. strongly overlapping/

2. approximated but not strongly overlapping/

3. distant from one another and not at all overlapping/

Pinna: a primary (first order) branch of a compound leaf.

#51. <Distinguishing the species of Woodsia:> /

1. the largest pinnae oblong or ovate-oblong, 1.5–2 times as long as broad, and the rachis and the undersides of the pinnae are densely scaly with 2–3 mm long, subulate, pale brown scales and flexuous hairs /

2. the largest pinnae triangular-ovate, 1–1.5 times as long as broad and the rachis and the undersides of the pinnae scale-less or with only short scales of about 1mm long, and few hairs /

#52. The venation of the lamina <whether reticulate>/

1. reticulate/

2. open <non-reticulate, free>/

#53. The veins of the ultimate pinnules <where terminating>/

1. terminating in the apices of their teeth/

2. mostly terminating in the notches between the teeth/

#54. <Heterosporous or homosporous:>/

1. homosporous /

2. heterosporous/

Homospory versus heterospory. These terms denote major differences in life cycles (q.v.). Typical ferns are homosporous, their sporophytes producing very numerous, tiny, air-borne spores which germinate to produce relatively inconspicuous but free-living prothalli which are at least potentially bisexual (i.e., capable of developing both antheridia and archegonia). In heterosporous forms (represented in Britain only by Azolla and Pilularia), however, the spores are of two kinds; viz., relatively few and relatively very large megaspores, in which develop the female prothalli producing only archegonia, and smaller microspores in which develop male prothalli producing only antheridia and motile antherozoids. Neither kind of prothallus becomes free living, being retained instead within the resistant wall of the spore; and the product of fertilization (the sporophyte plant) begins its development within the wall of the megaspore.

The life cycle common to all ferns involves a regular alternation of generations between gametophyte (sexual, haploid) and sporophyte (asexual, diploid) phases. The gametophyte produces male gametes (swimming antherozoids) in antheridia, and non-motile female gametes (egg cells) in flask-shaped archegonia. Fusion of an egg cell and an antherozoid within the archegonium results in a diploid zygote, which develops into the sporophyte. The sporophyte (represented by the familiar fern plant) ultimately produces sporangia, in which haploid, non-motile spores are produced. The life cycle is completed when the spores germinate and develop into haploid gametophytes. The fern gametophyte, termed the prothallus, is inconspicuous relative to the sporophyte, which constitutes the familiar fern plant.

#55. <Sporangial development, eu- or leptosporangiate:>/

1. eusporangiate/

2. leptosporangiate /

Eusporangiate versus leptosporangiate. Terms denoting differences in development and mature structure of the sporangia. In eusporangiate forms, they are short-stalked or sessile, relatively massive (generally well over 1 mm in diameter), the wall is several cells thick, and many spores develop in each. In leptosporangiate forms, on the other hand, they are borne on a slender stalk, relatively very small and delicate (less than 0.5 mm in diameter), the wall is only one cell thick, and few spores develop in each. Nearly all British ferns are leptosporangiate, representation of the eusporoangiate type beibg restricted to Botrychium, Ophioglossum and Osmunda.

Sporangium: a structure borne on the fern sporophyte, in which haploid spores are produced by meiotic cell division.

#56. The sporangia <nature and location>/

1. all alike, relatively massive, sessile and coalescing in two rows on the spikelike fertile component of the leaf <Ophioglossum>/

2. all alike, relatively massive, sub-sessile in two rows on the branches of the fertile component of the leaf <Botrychium>/

3. in paired sporocarps borne on the submerged ventral lobes of the first leaves of the branches, each sporocarp covered by a flange of the upper lobe, containing one sorus on a cylindrical receptacle and the sori of each pair either both containing megasporangia, or both with one microsporangium and one megasporangium (the former with 64 tiny microspores, the latter with a single large megaspore) <Azolla>/

4. in tiny, 4-compartmented, hairy, pill-like sporocarps at the bases of the subulate green leaves, the compartments each containing one sorus which splits longitudinally at maturity to release the sporangia in a mass of mucilage (the one-spored megasporangia borne below the many-spored microsporangia in the same sorus) <Pilularia>/

5. tiny and delicate, stalked, all alike, borne in aggregates <usually grouped in sori: typical of most ferns> /

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#57. The sporangia <marginal or superficial>/

1. marginal <arising at or near the edge of the lamina>/

2. superficial <arising on the lamina surface, some distance from its margin>/

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#58. The sporangia <with or without indusioid protection>/

1. exposed <with neither indusia nor false indusia>/

2. protected <usually with indusia or false indusia>/

#59. The sporangia <whether aggregated in sori>/

1. <at least at first> aggregated in <discrete> sori/

2. not aggregated into sori/

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

Sorus: a circumscribed group of sporangia (q.v.).

#60. The sori <at least when when young, round or elongate>/

1. sub-orbicular <more or less round in surface view, at least when young>/

2. elongated/

Sorus: a circumscribed group of sporangia (q.v.).

#61. The sori <whether becoming confluent>/

1. becoming confluent when mature/

2. remaining discrete at maturity/

#62. The sori <numbers>/

on either side of the mid-rib of the larger pinnules/

#63. The sori <whether sunken>/

1. perceptibly sunken and creating conspicuous rows of circular impressions on the upper surface of the lamina <Phymatodes>/

2. not sunken <only rarely associated with circular impressions on the upper surface of the lamina> /

#64. The sori <indusiate, pseudo-indusiate or naked>/

1. with a true indusium <only>/

2. with only a false indusium derived exclusively from the lamina margin/

3. protected by true and false indusia combined/

4. naked and neither indusiate nor pseudo-indusiate/

Indusium: a structure more or less covering or enclosing a sorus, in the form of a flap or a pocket, which protects the developing sporangia. Indusia vary in derivation, as well as in shape. Hypotheses concerning evolution of ferns have emphasized the difference between “true indusia”, representing outgrowths from the underside of the lamina adjacent to the sporangia, and “false indusia", representing modification of the leaf margin.

Sorus: a circumscribed group of sporangia (q.v.).

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#65. The indusia <shape> /

1. peltate /

2. reniform and attached at the indentation /

3. not reniform but flap-like from the base of the sorus, vaulted at first, later reflexed /

4. attached on one side along a vein <not reniform> /

5. consisting mainly of <reduced to> hairs /

6. projecting from the margins of the very thin lamina and enveloping the sori from their bases <entire or 2-lipped> /

Indusium: a structure more or less covering or enclosing a sorus, usually in the form of a flap or a pocket, which protects the developing sporangia. In some ferns the indusia have been shed by the time the spores are being shed, and in others they become reflexed or deformed. They vary in derivation, as well as in shape. Hypotheses concerning evolution of ferns have emphasized the difference between “true indusia”, representing outgrowths from the underside of the lamina adjacent to the sporangia, and “false indusia", representing modification of the leaf margin.

Sorus: a circumscribed group of sporangia (q.v.).

#66. The indusia <of Hymenophyllaceae, form> /

1. of two valves, without a protruding bristle /

2. tubular, with the apex of the elongated sporangial receptacle protruding as a bristle when mature /

Indusium: a structure more or less covering or enclosing a sorus, usually in the form of a flap or a pocket, which protects the developing sporangia. In some ferns the indusia have been shed by the time the spores are being shed, and in others they become reflexed or deformed. They vary in derivation, as well as in shape. Hypotheses concerning evolution of ferns have emphasized the difference between “true indusia”, representing outgrowths from the underside of the lamina adjacent to the sporangiua, and “false indusia", representing modification of the leaf margin.

#67. The valves <of the indusium, detailed shape: Hymenophyllum spp.>/

1. orbicular and toothed/

2. ovate and entire/

Indusium: a structure more or less covering or enclosing a sorus, usually in the form of a flap or a pocket, which protects the developing sporangia. In some ferns the indusia have been shed by the time the spores are being shed, and in others they become reflexed or deformed. They vary in derivation, as well as in shape. Hypotheses concerning evolution of ferns have emphasized the difference between “true indusia”, representing outgrowths from the underside of the lamina adjacent to the sporangia, and “false indusia", representing modification of the leaf margin.

#68. The indusia <details>/

#69. The false indusia <recurved blade margins covering the sori: interrupted or continuous>/

1. continuous along the blade segments/

2. interrupted on the individual blade segments/

Indusium: a structure more or less covering or enclosing a sorus, usually in the form of a flap or a pocket, which protects the developing sporangia. In some ferns the indusia have been shed by the time the spores are being shed, and in others they become reflexed or deformed. They vary in derivation, as well as in shape. Hypotheses concerning evolution of ferns have emphasized the difference between “true indusia”, representing outgrowths from the underside of the lamina adjacent to the sporangia, and “false indusia", representing modification of the leaf margin.

#70. The false indusia <shape>/

1. somewhat rectangular-elongate, not reniform/

2. reniform-orbicular/

#71. Paraphyses <presence presence in the sporangia>/

1. present in the sporangia/

2. absent/

Paraphysis: in this context, filamentous structures representing sterile sporangia.

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#72. The sporangia <sequence of development>/

1. developing sequentially within a sorus <sori “gradate”>/

2. not developing sequentially <sori “mixed”> /

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#73. The sporangial wall <thickness>/

1. of only one cell layer /

2. of several cell layers <eusporangiate ferns>/

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#74. The sporangial wall <presence of an annulus>/

1. incorporating a conspicuous annulus of thick-walled cells /

2. without an annulus/

Annulus: an arrangement of thick-walled cells, conspicuous under a dissecting microscope, associated with the dehiscence mechanism of a fern sporangium. Among British ferns, only the very peculiar and un-fernlike Azolla, Pilularia, Botrychium and Ophioglossum exhibit sporangia without annuli. An illustration accompanying the description of Dryopteris filix-mas exemplifies sporangia with the commonest type of annulus.

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#75. The sporangia <type of annulus> /

1. with an ‘annulus’ represented by a group of thick-walled cells on one side/

2. with an oblique annulus <and a stomium>/

3. with a vertical annulus <and a stomium> /

State 1 is associated with the relatively massive sporangia of some eusprangiate ferns (q.v.), and is exhibited here only by Osmunda. States 2 and 3 distinguish among those of the relatively tiny leptosporangiate forms.

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

Annulus: an arrangement of thick-walled cells, conspicuous under a dissecting microscope, associated with the dehiscence mechanism of a fern sporangium. Among British ferns, only the very peculiar and un-fernlike Azolla, Pilularia, Botrychium and Ophioglossum exhibit sporangia without annuli. An illustration accompanying the description of Dryopteris filix-mas exemplifies sporangia with the commonest type of annulus.

#76. The sporangia <dehiscence orientation>/

1. dehiscing via median slits transverse to the axis bearing them/

2. dehiscing by a slit running across the apex from the lateral annulus/

3. dehiscing horizontally by a transverse split <at right angles to the sporangial stalk> /

Annulus: an arrangement of thick-walled cells, conspicuous under a dissecting microscope, associated with the dehiscence mechanism of a fern sporangium. An illustration accompanying the description of Dryopteris filix-mas exemplifies sporangia with the commonest type of annulus.

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae.

#77. The annuli <of the sporangia, number of thick-walled cells>/

celled/

Potentially of wide application, but recorded only for Polypodium species.

Annulus: an arrangement of thick-walled cells, conspicuous under a dissecting microscope, associated with the dehiscence mechanism of a fern sporangium.

Sporangia(-ium): organs within which haploid, dispersible spores are produced, borne on the (diploid) sporophyte. Commonly on the underside of the leaf lamina, but sometimes on specialized leaves or pinnae. An illustration accompanying the description of Dryopteris filix-mas exemplifies sporangia with the commonest type of annulus.

#78. The mature spores <colour>/

1. yellow/

2. pale brown/

3. dark brown/

Spores: in this context, the small, dispersible, unicellular products of meiotic cell divisions within the sporangia of the fern sporophyte. Resembling pollen grains in the sporopollenin-containing wall, which is very resistant to decay and often ornamented in a manner characteristic of a species or genus. On germination, the spore gives rise to the prothallus (q.v.).

#79. The mature spores <whether echinate>/

1. echinate/

2. rugose/

#80. The mature spores <monolete or trilete>/

1. monolete/

2. trilete/

Monolete spores have one furrow, and are usually bean-shaped. Trilete spores have a tetrad scar comprising three furrows forming a Y, and may be detectably tetrahedral, triangular or more or less round.

Spores: in this context, the small, dispersible, unicellular products of meiotic cell divisions within the sporangia of the fern sporophyte. Resembling pollen grains in the sporopollenin-containing wall, which is very resistant to decay and often ornamented in a manner characteristic of a species or genus. On germination, the spore gives rise to the prothallus (q.v.).

#81. The mature spores <with or without a perispore>/

1. with a perispore/

2. without a perispore/

Perispore: a membrane surrounding some fern spores, which is differently patterned from the usual exine.

Spores: in this context, the small, dispersible, unicellular products of meiotic cell divisions within the sporangia of the fern sporophyte. Resembling pollen grains in the sporopollenin-containing wall, which is very resistant to decay and often ornamented in a manner characteristic of a species or genus. On germination, the spore gives rise to the prothallus (q.v.).

Prothallus

#82. Prothalli <endo- or exosporic>/

1. endosporic and reduced/

2. free-living /

Prothallus: the small plant formed by germination of a spore, on which develop the male gametes (antherozoids) in antheridia and/or the female gametes (egg cells) in archegonia. Comprising the sexual, haploid component of the life-cycle, the prothalli of most ferns are free-living, but in a few endosporic forms they are retained within the spores.

The life cycle common to all ferns involves a regular alternation of generations between gametophyte (sexual, haploid) and sporophyte (asexual, diploid) phases. The gametophyte produces male gametes (swimming antherozoids) in antheridia, and non-motile female gametes (egg cells) in flask-shaped archegonia. Fusion of an egg cell and an antherozoid within the archegonium results in a diploid zygote, which develops into the sporophyte. The sporophyte (represented by the familiar fern plant) ultimately produces sporangia, in which haploid, non-motile spores are produced. The life cycle is completed when the spores germinate and develop into haploid gametophytes. The fern gametophyte, termed the prothallus, is inconspicuous relative to the sporophyte, which constitutes the familiar fern plant.

#83. Prothalli <free-living, form>/

1. green and filamentous/

2. green, flat and strap-shaped/

3. green and fleshy /

4. non-green, subterranean, mycorrhizal/

Ecology, distribution, British status

#84. <Plants aquatic, helophytic or terrestrial:>/

1. aquatic/

2. helophytic <in wet ground>/

3. mesophytic /

#85. <Aquatics, floating or rooted:>/

1. floating/

2. rooted in the submerged substrate/

Note that some calcicole species are often found on mortared walls, far from their original chalk or limestone habitats.

#86. <Preferred substrates:>/

1. on base-rich substrates/

2. on neutral substrates/

3. on acid substrates/

Note that some calcicole species are often found on mortared walls, far from their original chalk or limestone habitats.

#87. <Habitat:>/

#88. <Status - native or naturalized:>/

1. native to the British Isles /

2. naturalized/

#89. <Summary of distribution in the British Isles:>/

Mostly quoted from Stace's (1997) account.

#90. <Distribution - Britain/Ireland: (B.S.B.I. data)>/

1. Britain <England, Scotland, Wales, Isle of Man, Channel Islands>/

2. Ireland <including Northern Ireland>/

Representing 2007 data, from records maintained by the Botanical Society of the British Isles.

WARNING. Geographical information can often facilitate pursuit of identifications, but must be used with caution. Recorded distributions may be incomplete, and plant distributions change with time. Identifications depending on the vice-county records may be wrong, and should be assiduously verified with reference to the full descriptions. In case of doubt, the Intkey 'tolerance' facility (q.v.) should be invoked.

It is axiomatic that no identification can be relied upon until it has been confirmed with reference to a detailed description.

#91. Britain: <distribution in the vice counties of Britain (B.S.B.I. data; see 'Notes'):>/

1. West Cornwall/

2. East Cornwall/

3. South Devon/

4. North Devon/

5. South Somerset/

6. North Somerset/

7. North Wiltshire/

8. South Wiltshire/

9. Dorset/

10. Isle of Wight/

11. South Hampshire/

12. North Hampshire/

13. West Sussex/

14. East Sussex/

15. East Kent/

16. West Kent/

17. Surrey/

18. South Essex/

19. North Essex/

20. Hertfordshire/

21. Middlesex/

22. Berkshire/

23. Oxfordshire/

24. Buckinghamshire/

25. East Suffolk/

26. West Suffolk/

27. East Norfolk/

28. West Norfolk/

29. Cambridgeshire/

30. Bedfordshire/

31. Huntingdonshire/

32. Northamptonshire/

33. East Gloucestershire/

34. West Gloucestershire/

35. Monmouthshire/

36. Herefordshire/

37. Worcestershire/

38. Warwickshire/

39. Staffordshire/

40. Shropshire/

41. Glamorgan/

42. Breconshire/

43. Radnorshire/

44. Carmarthenshire <Caerfyrddyn>/

45. Pembrokeshire/

46. Cardiganshire <Ceredigion>/

47. Montgomeryshire/

48. Merionethshire <Meirionydd>/

49. Caernarvonshire <Caernarfon>/

50. Denbighshire/

51. Flintshire/

52. Anglesey/

53. South Lincolnshire/

54. North Lincolnshire/

55. Leicestershire <with Rutland>/

56. Nottinghamshire/

57. Derbyshire/

58. Cheshire/

59. South Lancashire/

60. West Lancashire/

61. South-east Yorkshire/

62. North-east Yorkshire/

63. South-west Yorkshire/

64. Mid-west Yorkshire/

65. North-west Yorkshire/

66. Durham/

67. South Northumberland/

68. North Northumberland <Cheviot>/

69. Westmorland <with North Lancashire>/

70. Cumberland/

71. Isle of Man/

72. Dumfriesshire/

73. Kirkcudbrightshire/

74. Wigtownshire/

75. Ayrshire/

76. Renfrewshire/

77. Lanarkshire/

78. Peeblesshire/

79. Selkirkshire/

80. Roxburghshire/

81. Berwickshire/

82. East Lothian <Haddington>/

83. Midlothian <Edinburgh>/

84. West Lothian <Linlithgow>/

85. Fifeshire <with Kinross>/

86. Stirlingshire/

87. West Perthshire <with Clackmannan>/

88. Mid Perthshire/

89. East Perthshire/

90. Angus <Forfar>/

91. Kincardineshire/

92. South Aberdeenshire/

93. North Aberdeenshire/

94. Banffshire/

95. Moray <Elgin>/

96. East Inverness-shire <with Nairn>/

97. West Inverness-shire/

98. Argyll Main/

99. Dunbartonshire/

100. Clyde Isles/

101. Kintyre/

102. South Ebudes/

103. Mid Ebudes/

104. North Ebudes/

105. West Ross/

106. East Ross/

107. East Sutherland/

108. West Sutherland/

109. Caithness/

110. Outer Hebrides/

111. Orkney islands/

112. Shetland <Zetland>/

113. Channel Islands/

#92. Ireland: <distribution in the vice counties of Ireland (B.S.B.I. data; see 'Notes'):>/

1. South Kerry/

2. North Kerry/

3. West Cork/

4. Mid Cork/

5. East Cork/

6. Waterford/

7. South Tipperary/

8. Limerick/

9. Clare/

10. North Tipperary/

11. Kilkenny/

12. Wexford/

13. Carlow/

14. Leix <Queen's County>/

15. South-east Galway/

16. West Galway/

17. North-east Galway/

18. Offaly <King's County>/

19. Kildare/

20. Wicklow/

21. Dublin/

22. Meath/

23. West Meath/

24. Longford/

25. Roscommon/

26. East Mayo/

27. West Mayo/

28. Sligo/

29. Leitrim/

30. Cavan/

31. Louth/

32. Monaghan/

33. Fermanagh/

34. East Donegal/

35. West Donegal/

36. Tyrone/

37. Armagh/

38. Down/

39. Antrim/

40. Londonderry/

Classification

#93. Family <C.T.W.>/

1. Azollaceae (C.T.W.)/

2. Hymenophyllaceae (C.T.W.)/

3. Marsileaceae (C.T.W.)/

4. Ophioglossaceae (C.T.W.)/

5. Osmundaceae (C.T.W.)/

6. Polypodiaceae (C.T.W.)/

#94. Family <Swale and Hassler>/

1. Adiantaceae (Swale and Hassler)/

2. Aspleniaceae (Swale and Hassler)/

3. Athyriaceae (Swale and Hassler)/

4. Azollaceae (Swale and Hassler)/

5. Blechnaceae (Swale and Hassler)/

6. Cystopteridaceae (Swale and Hassler)/

7. Dryopteridaceae (Swale and Hassler)/

8. Hymenophyllaceae (Swale and Hassler)/

9. Hypolepidaceae (Swale and Hassler)/

10. Marsileaceae (Swale and Hassler)/

11. Notholaenaceae (Swale and Hassler)/

12. Ophioglossaceae (Swale and Hassler)/

13. Osmundaceae (Swale and Hassler)/

14. Polypodiaceae (Swale and Hassler)/

15. Pteridaceae (Swale and Hassler)/

16. Thelypteridaceae (Swale and Hassler)/

17. Trichomanaceae (Swale and Hassler)/

18. Woodsiaceae (Swale and Hassler)/

19. Onocleaceae (Swale and Hassler)/

20. Drynariaceae (Swale and Hassler)/

#95. Family <Stace>/

1. Ophioglossaceae (Stace)/

2. Osmundaceae (Stace)/

3. Adiantaceae (Stace)/

4. Pteridaceae (Stace)/

5. Marsiliaceae (Stace)/

6. Hymenophyllaceae (Stace)/

7. Polypodiaceae (Stace)/

8. Dicksoniaceae (Stace)/

9. Dennstaedtiaceae (Stace)/

10. Thelypteridaceae (Stace)/

11. Aspleniaceae (Stace)/

12. Woodsiaceae (Stace)/

13. Dryopteridaceae (Stace)/

14. Blechnaceae (Stace)/

15. Azollaceae (Stace)/

#96. Order <Swale and Hassler>/

1. Aspleniales (Swale and Hassler)/

2. Athyriales (Swale and Hassler)/

3. Dennstaedtiales (Swale and Hassler)/

4. Dryopteridales (Swale and Hassler)/

5. Hymenophyllales (Swale and Hassler)/

6. Marsileales (Swale and Hassler)/

7. Osmundales (Swale and Hassler)/

8. Polypodiales (Swale and Hassler)/

9. Psilotales (Swale and Hassler)/

10. Pteridales (Swale and Hassler)/

#97. <Hybrids:>/

Comments

#98. <Comments:>/

Special key character

#99. The pinnae of the sterile leaves <attachment>/

1. much narrowed basally, attached over only a short width <B. cordatum>/

2. with broadened, contiguous bases <B. spicant>/


To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. British ferns (Filicopsida). Version: 4th January 2012. http://delta-intkey.com’.

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