Hymenophyllum australe

Hymenophyllum australe, commonly known as austral filmy fern,[1] is a relatively large rupestral and epiphytic fern, indigenous to eastern Australia[2] and New Zealand.[3] It belongs to the unique Hymenophyllum genus (filmy ferns), which are characterised by their thin membranous fronds that are seldom more than one cell thick, with the exception of regions over and around veins.[2] Hymenophyllum australe is distinctive in that the fronds are typically thicker than other Hymenophyllum species, often being up to 2-3 cells thick.[4][5]

Austral filmy-fern
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Class: Polypodiopsida
Order: Hymenophyllales
Family: Hymenophyllaceae
Genus: Hymenophyllum
Species:
H. australe
Binomial name
Hymenophyllum australe
Synonyms

Mecodium australe Hymenophyllum atrovirens

Hymenophyllum australe is inconspicuous and will typically form matted patches together with mosses and liverworts.[1] In Australia it takes on an epiphytic approach, commonly seen to clothe roots, trunks and rocks to form a dense mat of foliage;[1] while in New Zealand it adopts a more rheophytic approach, preferring rocks or tree trunks in or close to water.[3][6]

It has dark green fronds, which are distinctly deltoid in shape, with entire ultimate segment margins, each containing a single conspicuous vein.[2] It is recognised by its winged fronds, which are initially relatively broad (several millimetres wide) but gradually taper from the rachis along the stipe.[7]

Description

Hymenophyllum australe are rupestral or epiphytic ferns. The rhizomes are long-creeping, fine (typically 0.2-0.5 mm in diameter), branched and possess bare scattered hairs typically clustered near the base of the stipe.[3][2] Stomata are absent.[2]

Characteristic of the Hymenophyllum genus, the sori are terminal on segments (see sketch below) and encompass a two-lipped indusium (protective cover),[8] which often has notched margins.[1] The sori are numerous and borne singly or paired.[2] The receptacle is short and enclosed within indusial flaps. The species is homosporous,[3] with spores trilete, greenish and slightly roughened.[8]

The stipes are winged almost to the base, often crinkled and emanate at intervals along the rhizome.[1][2][9] The fronds are dark green, dull and membranous, ranging in size from 38-210 mm long;[2] they are triangular to ovate in shape and pinnate to tripinnate.[1] The rachises are winged, glabrous, dark brown proximally and pale brown distally.[3] The ultimate lamina segments are narrowly oblong and have a spreading finger-like appearance; the margins are entire, with each ultimate segment containing a single conspicuous vein.[9][3]

Taxonomy and naming

Hymenophyllum australe was first formally described in 1810 by Carl Ludwig Willdenow in the published Species Plantarum Edition 4,[10][11] under the basionym of Mecodium australe.[9][11]

The botanical genus name Hymenophyllum is derived from the Greek hymen, meaning membrane, and phullon, a leaf, referring to the delicate membranous leaf,[2] while the specific epithet, australe, is derived from the Latin australis, meaning southern, in reference to its occurrence in Australia and New Zealand.[3]

Notably, New Zealand populations of Hymenophyllum australe were previously divided into a separate species, Hymenophyllum atrovirens, and interpreted as endemic to New Zealand.[12][13] However, given the absence of distinguishable morphological characters,[5] in addition to recent molecular evidence demonstrating pronounced similarity of the chloroplast DNA sequences of the Australian and New Zealand ferns,[14] Hymenophyllum atrovirens is now considered conspecific with Hymenophyllum australe.[3]

Hymenophyllum atrovirens was initially described in 1845 by English botanist William Colenso in his collections from Lake Waikaremoana in 1841.[15][14]

Distribution

Hymenophyllum australe is a common fern species of eastern Australia, principally located in the rainforests and fern gullies. It is present in Victoria, from the Otways through to Gippsland[2] and was formally present on the Mornington Peninsula, but recently appears extinct in this area owing to bushfires.[16]

It is also found in Tasmania, southern Queensland and New South Wales, in particular the Blue Mountains area.[2][1] Hymenophyllum australe is also present on both the north and south islands of New Zealand, although there it is less common than in Australia.

In Tasmania and New Zealand it has been noted the wings of the fronds are typically smaller and the segments less wrinkled.[9]

Sketch of Hymenophyllum australe frond. Highlighting the single conspicuous single vein in each ultimate segment and terminal sori.
Hymenophyllum australe, picture by Robert Wiltshire.

.

Regions in New Zealand where Hymenophyllum australe has been recognised
North Island Northland, Auckland, Volcanic Plateau, Gisborne, Taranaki, Southern North Island[3]
South Island Western Nelson, Canterbury, Otago, Fiordland, Stewart Island[3]
Regions in Australia where Hymenophyllum australe has been recognised
Victoria Gippsland Plain, Otway Plain, Otway Ranges, Warrnambool Plain, Central Victorian Uplands, East Gippsland Lowlands, East Gippsland Uplands, Wilsons Promontory, Highlands-Southern Fall, Highlands-Northern Fall, Strzelecki Ranges, Highlands-Far East, Victorian Alps[16]
Queensland South-east[2]
New South Wales North Coast, Central Coast, South Coast, Central Tablelands[17]
Tasmania Tasmanian Southern Ranges, Tasmanian West, Tasmanian South East, Ben Lomond, Circular Head, Tasmanian Northern Slopes, Furneaux, Tasmanian Central Highlands[18]

Habitat

Filmy ferns are typically small in size and limited to wet or misty areas due to the thin, delicate nature of their fronds.[1][19] Water is rapidly lost under a dry atmosphere and in consequence Hymenophyllum australe will shrivel and collapse[1] as filmy-ferns possess no strengthening tissues in their fronds; being entirely dependent on water pressure to maintain turgidity.[4] As a result, these fragile ferns grow optimally where the air is moist.[19]

In New Zealand, Hymenophyllum australe is heavily constrained to growing on rocks, or rarely low on tree trunks, either partially submerged or close to flowing water in shaded habitats.[3] It almost displays a rheophytic habit and is seldom found away from waterways.[20]

Conversely in Australia the species grows in a much broader range of habitats, expanding to rock further away from water and additionally as an epiphyte.[3][1] It is common to wet forests and routinely forms curtains on tree-trunks, logs, wet rocks or on the walls of caves, given there is sufficient light present.[1] In Australia, Hymenophyllum australe is found to display a strong association with tree-fern trunks, commonly perceived to adorn tree-ferns from top to bottom.[8] In Tasmania, Hymenophyllum australe was found to exhibit a significant preference to grow on the trunks of the more prevalent Dicksonia antarctica than the trunks of the rarer Cyathea cunninghamii tree-ferns.[21]

Reproduction

Sexual reproduction

Like all ferns, Hymenophyllum australe has a life cycle with two distinct phases: a minor haploid gametophyte stage, which grows from spores and produces the gametes, and a sporophyte stage which is diploid and yields spores from the sporangia.[1]

The gametophytic generation begins with the formation of spores from the sporangia on the leaf of a sporophyte, under favourable conditions (adequate moisture, temperature, pH range and light intensity[22]) these spores will germinate and subsequently develop into a filamentous prothalli (or gametophyte).[2]

The prothallus in Hymenophyllum australe (including all Hymenophyllum species) is long and narrow and often referred to as ribbon-like.[23][24] This is atypical of the archetypal heart-shaped prothallus seen in other ferns.[24][4] The prothallus harbours sporadic marginal archegonial cushions[24] and this is where the archegonia are borne, while the antheridia are borne on slender branches on the basal margins of the prothallus.[23]

In the presence of water, spores germinate following a typical fern progression, with the antheridia trapped under the prothallus bursting to release the sperm cells. A chemical signal (sperm chemotaxis) is released from the archegonia which attracts the motile sperm cells towards it. Once the sperm cells reach the archegonium, they open and enable the male gamete to travel down to the ovum, with which it unites to induce fertilisation and form a zygote.

This fertilised zygote is diploid and develops into an embryo and sporophyte, or ‘true fern’ that is most readily recognised, while remaining embedded in the prothallus. The sporophyte is dependent on the prothallus for nutrition (parasitic) until the embroyo forms its first roots and leaves, whereupon the sporophyte becomes independent and the prothallus subsequently dies.[2] The cycle is complete when spores are produced on the sporophyte.

Notably, as in all ferns, water is required for successful sexual reproduction, with the fusion of the gametes entirely dependent on the availability of free water.[2]

Asexual reproduction

Both the gametophyte and sporophyte are capable of vegetative reproduction. In the gametophyte stage this is typically through regeneration of fresh prothalli from older ones, but it can also occur through gemmae which are more organised means of vegetative propagation.[24]

It has been recognised that adverse growing conditions, such as drying, promotes abundant formation of gemmae, as vegetative reproduction does not involve the fusion of gametes and hence does not require free water.[24]

Conservation status

Hymenophyllum australe in Australia is considered locally common within its preferred growing conditions.[25][26][27] However, in New Zealand the conservation status of Hymenophyllum australe was reassessed in 2012 using the New Zealand Threat Classification System (NZTCS) to be "at risk to naturally uncommon".[28]

Cytology

Chromosome number = 36 (N=36).[29]

Further reading
  • Chloroplast Similarity between H.australe and H.atrovirens: Perrie, LR; Shepherd, LD; De Lange, PJ; Batty, EL; Ohlsen, DJ; Bayly, MJ; Brownsey, PJ (2013). "Hymenophyllum pluviatile, a new and uncommon fern from New Zealand". New Zealand Journal of Botany. 51 (4): 308–320. doi:10.1080/0028825x.2013.834830.
  • Key to Tasmanian Hymenophyllum species
  • Key to the New Zealand Filmy Ferns (Hymenophyllaceae)
  • Atlas of Living Australia occurrence data
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References
  1. Jones, David L; Clemesha, Steven C (1976). Australian ferns and fern allies. Terrey Hills: Reed Publishing Ltd. pp. 9, 8, 64, 69, 70. ISBN 0589071971.
  2. Duncan, Betty D; Isaac, Golda (1986). Ferns and allied plants of Victoria, Tasmania and South Australia. Australia: Melbourne University Press. pp. 2, 3, 78, 81, 83, 84. ISBN 0522842623.
  3. Brownsey, Patrick J; Perrie, Leon R (2016). Flora of New Zealand: Hymenophyllaceae. Lincoln, New Zealand: Manaaki Whenua Press. pp. 8–10. doi:10.7931/B1QP4Z. ISBN 9780478347876.
  4. Garrett, M. (1986, December). "Fairies of the Fern World", Newsletter Number 35, pp. 9. Retrieved from URL (https://www.verdigris.com.au/default.aspx?hid=310)
  5. Ebihara, Atsushi; Nitta, Joel H (2010). "The Hymenophyllaceae of the Pacific Area. 2. Hymenophyllum (Excluding Subgen. Hymenophyllum)" (PDF). Bulletin of the National Museum of Nature and Science. Series B, Botany. 36: 51 – via Kahaku.
  6. "Hymenophyllum australe | New Zealand Plant Conservation Network". www.nzpcn.org.nz. Retrieved 2019-12-07.
  7. Perrie, LR; Shepherd, LD; de Lange, PJ; Batty, EL; Ohlsen, DJ; Bayly, MJ; Brownsey, PJ (2013). "Hymenophyllum pluviatile, a new and uncommon fern from New Zealand". New Zealand Journal of Botany. 51 (4): 308–320. doi:10.1080/0028825x.2013.834830. ISSN 0028-825X.
  8. Andrews, S B (1990). Ferns of Queensland: A handbook to the ferns and fern allies. Queensland: Queensland Department of Primary Industries. p. 177. ISBN 0724232249.
  9. Wakefield, Norman Arthur; Willis, James Hamlyn (1975). Ferns of Victoria and Tasmania. Melbourne: Field Naturalists Club of Victoria. pp. 3, 5. ISBN 0959807411.
  10. Linné, Carl von; Willdenow, Karl Ludwig; Link, Heinrich Friedrich; Schwägrichen, Christian Friedrich; Nauck (Firm), G. C. (1797–1830). Caroli a Linné Species plantarum :exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. v.5:pt.1 (Ed. 4., post Reichardianam quinta ed.). Berolini: Impensis G.C. Nauk.CS1 maint: date format (link)
  11. "Vascular Plants". biodiversity.org.au. Retrieved 2019-12-07.
  12. Allan, H. H. (Harry Howard), 1882-1957. (1982). Flora of New Zealand. Psilopsida, Lycopsida, Filicopsida, Gymnospermae, Dicotyledones. Government Printer. ISBN 0-477-01056-3. OCLC 760926043.CS1 maint: multiple names: authors list (link)
  13. Brownsey, P. J.; Given, D. R.; Lovis, J. D. (1985). "A revised classification of New Zealand pteridophytes with a synonymic checklist of species". New Zealand Journal of Botany. 23 (3): 431–489. doi:10.1080/0028825x.1985.10425348. ISSN 0028-825X.
  14. Perrie, LR; Shepherd, LD; de Lange, PJ; Batty, EL; Ohlsen, DJ; Bayly, MJ; Brownsey, PJ (2013). "Hymenophyllum pluviatile, a new and uncommon fern from New Zealand". New Zealand Journal of Botany. 51 (4): 308–320. doi:10.1080/0028825x.2013.834830. ISSN 0028-825X.
  15. Colenso, W. (1845). A classification and description of some newly-discovered ferns : collected in the northern island of New Zealand in the summer of 1841-2 /. Launceston, V.D. Land: Printed at the office of the Launceston examiner. doi:10.5962/bhl.title.132534.
  16. "Flora of Victoria". vicflora.rbg.vic.gov.au. Retrieved 2019-12-07.
  17. "PlantNET - FloraOnline". plantnet.rbgsyd.nsw.gov.au. Retrieved 2019-12-07.
  18. Herbaria, jurisdiction:Australian Government Departmental Consortium;corporateName:Council of Heads of Australasian. "Partners". avh.ala.org.au. Retrieved 2019-12-07.
  19. Chinnock, R J; Heath, Eric W (1987). Common Ferns and Fern Allies in New Zealand. Auckland, New Zealand: Reed Methuen Publishers Ltd. p. 28. ISBN 0474002934.
  20. "Hymenophyllum australe | New Zealand Plant Conservation Network". www.nzpcn.org.nz. Retrieved 2019-12-07.
  21. ROBERTS, NINA R.; DALTON, PATRICK J.; JORDAN, GREGORY J. (2005). "Epiphytic ferns and bryophytes of Tasmanian tree-ferns: A comparison of diversity and composition between two host species" (PDF). Austral Ecology. 30 (2): 146–154. doi:10.1111/j.1442-9993.2005.01440.x. ISSN 1442-9985.
  22. Miller, John H. (1968). "Fern gametophytes as experimental material". The Botanical Review. 34 (4): 361–440. doi:10.1007/bf02859133. ISSN 0006-8101.
  23. Stone, IG (1965). "The gametophytes of the Victorian Hymenophyllaceae". Australian Journal of Botany. 13 (2): 195. doi:10.1071/bt9650195. ISSN 0067-1924.
  24. Nayar, B K; Kaur, S (1971). "Gametophytes of Homosporous Ferns". Botanical Review. 37 (3): 356–359, 376. JSTOR 4353813.
  25. ".: Hymenophyllum australe :". fe.yarraranges.vic.gov.au. Retrieved 2019-12-07.
  26. "Flora Recovery Plan: Threatened Tasmanian Ferns" (PDF). Department of the Environment and Energy. Retrieved 2019-12-07.
  27. Environment, jurisdiction=Commonwealth of Australia; corporateName=Department of the. "Threatened Species List". www.environment.gov.au. Retrieved 2019-12-07.
  28. De Lange, Peter J. (Peter James), author. Conservation status of New Zealand indigenous vascular plants, 2012. OCLC 992779428.CS1 maint: multiple names: authors list (link)
  29. Brownlie, G. Chromosome numbers in some Pacific Pteridophyta. OCLC 79659531.


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