Hymenophyllum axsmithii

Hymenophyllum axsmithii; Temporal range: Eocene (Ypresian); ~51–49 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Division:	Polypodiophyta
Class:	Polypodiopsida
Order:	Hymenophyllales
Family:	Hymenophyllaceae
Genus:	Hymenophyllum
Subgenus:	† Hymenophyllum subg. Sphaerocionium
Species:	†H. axsmithii
Binomial name
	†Hymenophyllum axsmithii; Pigg et al.

Last updated November 22, 2024

Hymenophyllum axsmithii is an extinct species of fern in the family Hymenophyllaceae related to the modern hayscented ferns. The species is known from fossil fronds found in early Eocene sites of northern Washington state, United States, and central British Columbia, Canada. The species is included in Hymenophyllum subgenus Sphaerocionium, with a suggestion to be closest to a group of tropical species in the subgenus that are all specialized as sheltered epiphytes.

Distribution

Hymenophyllum axsmithii fossils have been recovered from a single site in the Eocene Okanagan Highlands of Central British Columbia and northeast central Washington state. Both of the described specimens are from the Klondike Mountain Formation in Northern Ferry County, Washington, being recovered from the "Boot Hill" site B4131 in Republic, Washington.^[1]

History and classification

Fern fossils of the subclass Polypodiidae, commonly called leptosporangiate ferns, have been reported in the Eocene Okanagan Highlands since the late 1890s, and the first fertile fond material report came from Edward W. Berry (1926).^[1] More recently land ferns are regularly but briefly mentioned in overviews of the Eocene Okanagan Highlands, no detailed descriptive work as happened. The Republic fossils were studied subsequently by a group of paleobotanists led by Kathleen B. Pigg, with the 2021 type description of the species being published in the International Journal of Plant Sciences .^[1] They designated two type specimens at the time of publication, the holotype "SR 05-15-13" which was accessioned in the Stonerose Interpretive Center paleobotanical collection, while the paratype "UWBM 77726a" was part of the Burke Museum of Natural History and Culture paleontology collection. The holotype and paratype were collected from the Klondike Mountain Formations "Boot Hill" site "B4131". The team coined the specific epithet axsmithii as a patronym honoring Brian J. Axsmith for his many works in paleobotany, including the description of the oldest member of Hymenophyllaceae the Triassic Hopetedia praetermissa .^[1]

The group placed the new species into the modern genus Hymenophyllum based on the thin fronds plus placement and shape of the preserved sori indusia. The placement of the fossil sori are along the pinnae edges, and each of the sori are enclosed by a bivalved globose indusia, occasionally surrounded by trichomes. The fronds are distinctly thin as in the modern species, with similar leaf shapes and dissection.^[1] The genus as of 2023 included approximately 430 species which are mostly found in the tropics globally, but having a Cosmopolitan distribution.^[2] Of the species in Hymenophyllum, H. axsmithii is most similar in its known morphology to a group of Hymenophyllum subg. Sphaerocionium species found in the neotropics.^[1] The species, H. dependens , H. lobatoalatum , H. plumieri , H. plumosum , H. pyramidatum , and H. verecundum are native to central and South America.^[1]Hymenophyllum axsmithii has been noted one of the oldest unequivocal fossil species of Hymenophyllum, and the only firm record from the Cenozoic.^[2]^[3]

Description

Dennstaedtia christophelii is known only from leaf frond fossils, and as such the rhizome anatomy and spore morphology are unknown. The two described fronds are both incomplete, with the fertile frond section measuring 4.0 cm × 2.8 cm (1.6 in × 1.1 in) with 6 pairs of pinnae, and the vegetative specimen being approximately 3.0 cm (1.2 in) long. The rachis has a slightly ribbed appearance and there are narrow laminae wings along the plane of pinnae running up both sides of it.^[1]

The petiole is missing on both specimens, while the rachis which is 1.3 mm (3⁄50 in) at its widest and terminating in the uppermost crosier. The sterile frond fragment is very similar to the fertile fragment in pinnae shape and vascularization. The leaves are weakly bipinnate, with the laminae modified into separated pinnules, which in turn are weakly lobed. The pinnules are oriented in an alternating pattern along the rachis, and fertile pinnules alternate with inertial ones. The thin pinnules have bifurcating veins running from the rachis at the lamina base apically. The veins fork up to three times with each veinlet diverging into a separate lobe and all terminating at lope tips. The basal most fork in the laminae arches to run parallel to the rachis, while all branches fork off basal sides of the main veins. The amount of vein forking in each pinnules decreases the closer the pinnule is to the apex. Scattered trichomes are found along the edges of the pinnule, often associated with sori.^[1]

Sori are located in funnel shaped receptacles which are flush with the pinnae surface. The sori are surrounded by globose bivalved indusia of about 1 mm × 1 mm (0.039 in × 0.039 in) located along the apical and basal margins of fertile pinnules. Where preserved the sori are comprised of numerous sporangia. Within each sporangia, the annulus is between 10 and 12 cells wide and are interpreted to have been sessile, typical for the family. Examination of the fossils via an environmental scanning electron microscope showed that some of the sporangia enclosed between 7 and 10 dark ovoid structures. While no details of the structures was discernable, the location suggests them to be spore casts.^[1]

Paleoecology

One Hymenophyllum is native to the greater Washington and British Columbia areas, H. wrightii which is confined to the coast of the Pacific Northwest Coast ecoregion,^[1] and placed in H. subg. Mecodium.^[4] Pigg et al noted the probable affinity to a group of H. subg. Sphaerocionium species. These species are all restricted to humid mountain locations in the neotropics with epiphyte substrate specialization for protected areas such as rock ledges or under tree branches.^[1] Pigg et al noted that despite the modern relatives epiphytic nature, the possibility Hymenophyllum axsmithii was an epiphyte or not will depend on more fossils being found and described; in particular the rhizome and root structure will be key to determining where in the Republic paleoforest it lived.^[1]

Paleoenvironment

The Republic sites are part of a larger fossil site system collectively known as the Eocene Okanagan Highlands. The highlands, including the Early Eocene formations between Driftwood Canyon at the north and Republic at the south, have been described as one of the "Great Canadian Lagerstätten "^[5] based on the diversity, quality and unique nature of the paleofloral and paleofaunal biotas that are preserved. The highlands temperate biome preserved across a large transect of lakes recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines.^[5] The warm temperate highland floras in association with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents. This is due to the more seasonally equitable conditions of the Early Eocene, resulting in much lower seasonal temperature shifts. However, the highlands have been compared to the upland ecological islands of the Virunga Mountains within the African rift valleys Albertine Rift.^[6]

The Klondike Mountain Formation represents an upland lake system that was surrounded by a warm temperate ecosystem^[1] with nearby volcanism^[5] dating from during and just after the early Eocene climatic optimum. The Okanagan Highlands likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable.^[7] The paleoforest surrounding the lakes have been described as precursors to the modern temperate broadleaf and mixed forests of Eastern North America and Eastern Asia. Based on the fossil biotas the lakes were higher and cooler then the coeval coastal forests preserved in the Puget Group and Chuckanut Formation of Western Washington, which are described as lowland tropical forest ecosystems. Estimates of the paleoelevation range between 0.7 and 1.2 km (0.43 and 0.75 mi) higher than the coastal forests. This is consistent with the paleoelevation estimates for the lake systems, which range between 1.1 and 2.9 km (1,100 and 2,900 m), which is similar to the modern elevation 0.8 km (0.50 mi), but higher.^[7]

Estimates of the mean annual temperature have been derived from climate leaf analysis multivariate program (CLAMP) analysis and leaf margin analysis (LMA) of the Republic paleoflora. The CLAMP results after multiple linear regressions gave a mean annual temperature of approximately 8.0 °C (46.4 °F), with the LMA giving 9.2 ± 2.0 °C (48.6 ± 3.6 °F).^[7] A bioclimatic-based estimate based on modern relatives of the taxa found at Republic suggested mean annual temperatures around 13.5 ± 2.2 °C (56.3 ± 4.0 °F).^[7] This is lower than the mean annual temperature estimates given for the coastal Puget Group, which is estimated to have been between 15 and 18.6 °C (59.0 and 65.5 °F). The bioclimatic analysis for Republic suggests a mean annual precipitation amount of 115 ± 39 cm (45 ± 15 in).^[7]

Related Research Articles

A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. 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. "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.

Cyathea affinis is a variable species of tree fern native to Fiji, Samoa, the Cook Islands, Austral Islands, Tahiti, and the Marquesas Islands. The trunk of this plant is erect and 2–6 m tall. Fronds are bipinnate and 2–3 m in length. The rachis and stipe are pale to brown in colour, or flushed with red towards the pinnule rachis. The stipe is sparsely covered in narrow basal scales, which are pale to dark and have broad fragile edges. Characteristically of this species, the lowest one or two pairs of pinnae may be slightly reduced and occur towards the base of the stipe. Sori are located near the pinnule midvein and are partially or fully covered by indusia, which open towards the pinnule margin.

Gymnosphaera atropurpurea, synonyms Alsophila atropurpurea and Cyathea atropurpurea, is a species of tree fern native to the islands of Luzon, Mindanao, Leyte and Mindanao in the Philippines, where it grows in forest at above 1000 m. The erect trunk is slender and may be up to 3 m tall. Fronds are bipinnate and 1–2 m long. Characteristically of this species, the final pair of pinnae are usually reduced and occur towards the base of the stipe. These, along with the stipe bases, are persistent and retained around the trunk long after withering. The stipe itself is dark and covered with scales, which are either small, dull and brown or large, dark and glossy. Sori occur near the midvein of fertile pinnules and lack indusia. Fertile pinnules are notably smaller than sterile ones.

Alsophila coactilis, synonym Cyathea coactilis, is a rare species of tree fern known only from the southern highlands of Papua New Guinea, where it grows in alpine shrubland at an altitude of about 3000 m. The trunk is erect and 2–3 m tall. Fronds are bi- or tripinnate and usually 1–2 m long. Characteristically of this species, they occur in two whorls of about ten fronds each. The underside of the rachis is covered with small, pale scales. The stipe is covered with pale scales that have dark, narrow and fragile edges. Sori are round and are covered by thin indusia that are cup-like in appearance. They occur near the fertile pinnule midvein.

The Hymenophyllaceae, the filmy ferns and bristle ferns, are a family of two to nine genera and about 650 known species of ferns, with a subcosmopolitan distribution, but generally restricted to very damp places or to locations where they are wetted by spray from waterfalls or springs. Fossil evidence shows that ferns of the family Hymenophyllaceae have existed since at least the Upper Triassic.

Hymenophyllum is a genus of ferns in the family Hymenophyllaceae. Its name means "membranous leaf", referring to the very thin translucent tissue of the fronds, which gives rise to the common name filmy fern for this and other thin-leaved ferns. The leaves are generally only one cell thick and lack stomata, making them vulnerable to desiccation. Consequently, they are found only in very humid areas, such as in moist forests and among sheltered rocks. They are small and easy to overlook.

Hymenophyllum nephrophyllum, the kidney fern, is a filmy fern species native to New Zealand. It commonly grows on the forest floor of open native bush. Individual kidney-shaped fronds stand about 5–10 cm tall. In hot weather they shrivel up to conserve moisture, but open up again when the wet returns. This species has very thin fronds which are only four to six cells in thickness. In the Māori language they are also called raurenga.

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.

Hymenophyllum flabellatum, the shiny filmy-fern, is a species of fern in the family Hymenophyllaceae. This delicate fern is commonly epiphytic and is between 5 and 25 cm in length. It is distinct, with its thin, one-celled thick, membranous leaves. It is from the family Hymenophyllaceae and is dispersed world wide. The species is dispersed highly throughout Tasmanian rainforests and in the south east of mainland Australia, with small pockets of the population seen in northern Queensland.

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.

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.

Myriopteris lanosa, the hairy lip fern, is a moderately-sized fern of the eastern United States, a member of the family Pteridaceae. Its leaves and stem are sparsely covered in hairs, but lack scales, hence its common name. One of the cheilanthoid ferns, it was usually classified in the genus Cheilanthes until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows in shallow, dry, soil, often in rocky habitats.

Myriopteris alabamensis, the Alabama lip fern, is a moderately-sized fern of the United States 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 alabamensis until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows in shade on limestone outcrops.

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.

Myriopteris allosuroides is a moderately-sized fern endemic to Mexico, a member of the family Pteridaceae. Unlike many members of its genus, its rachides are grooved on the upper surface and largely free of hairs or scales. One of the cheilanthoid ferns, it was usually classified in the genera Cheilanthes or Pellaea until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on dry, rocky slopes over acidic, particularly basaltic, rock.

Hymenophyllum rarum, the narrow filmy-fern, is a species of fern from the family Hymenophyllaceae. This thin-leaved fern is commonly found in New Zealand and Tasmania, growing in patches on rocks and is epiphytic on trees and tree ferns, growing in moist gullies or rainforests. A rather drought tolerant species often found at exposed sites ranging from coastal to montane areas. Forming extensive, interwoven and creeping patches with its thin long (creeping) rhizomes sparsely covered in red-brown hairs, easily recognised by its membranous grey-green fronds, the smooth margins of the pinnae, ultimate segments and indusia; and by the sunken sori in the uppermost segments of the uppermost pinnae. The species can be found throughout Tasmanian rainforests as well as occurring in New South Wales, Victoria and New Zealand on the North and South Islands as well as, Stewart, Chatham and Auckland Islands.

Hymenophyllum peltatum, also known as alpine filmy-fern, is a species of filmy fern widely distributed across Australia, New Zealand, South Africa, South America. It is predominantly a rainforest species with delicate foliage arrangements. Members of the Hymenophyllaceae family display almost translucent fronds, bearing thickness of just a single cell.

Dickwhitea is an extinct morphogenus of lady fern containing a single morphospecies Dickwhitea allenbyensis. The species is known from permineralized remains recovered from the Princeton Chert in British Columbia, Canada. Rhizomes of Dickwhitea are noted for having a sympodial vascular architecture notably similar to Ginkgo biloba and Sequoia sempervirens.

Dennstaedtia christophelii is an extinct species of fern in the family Dennstaedtiaceae related to the modern hayscented ferns. The species is known from fossil fronds found in early Eocene sites of northern Washington state, United States and central British Columbia, Canada. The species is suggested to be closest to a Neotropical "Patania" clade and specifically the species Dennstaedtia producta and Dennstaedtia mathewsii.

References

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pigg, K. B.; DeVore, M. L.; Greenwood, D. R.; Sundue, M. A.; Schwartsburd, P.; Basinger, J. F. (2021). "Fossil Dennstaedtiaceae and Hymenophyllaceae from the Early Eocene of the Pacific Northwest". International Journal of Plant Sciences. 182 (9): 793–807. doi:10.1086/715633. S2CID 239036762.
1 2 Li, Y.; Wang, Y.-D.; Nosova, N.; Lu, N.; Xu, Y.-Y. (2022). "Filmy Ferns (Hymenophyllaceae) and Associated Spike-Mosses (Selaginellaceae) from the Mid-Cretaceous Kachin Amber, Myanmar". Biology. 11 (11). 1629. doi: 10.3390/biology11111629 . PMC 9687414 . PMID 36358330.
↑ Li, Y.; Ebihara, A.; Nosova, N.; Tan, Z.-Z.; Cui, Y.-M. (2023). "First Fossil Record of Trichomanessensu lato (Hymenophyllaceae) from the Mid-Cretaceous Kachin Amber, Myanmar". Life. 13 (8). 1709. Bibcode:2023Life...13.1709L. doi: 10.3390/life13081709 . PMC 10455793 . PMID 37629566.
↑ Chang, Z.X.; Hsu, T.C.; Kuo, L.Y. (2022). "Hymenophyllum chamaecyparicola (Hymenophyllaceae), a new filmy fern species from Taiwan". PhytoKeys (23): 23–34. doi: 10.3897/phytokeys.204.86045 . PMC 9848887 . PMID 36760617.
1 2 3 Archibald, S.; Greenwood, D.; Smith, R.; Mathewes, R.; Basinger, J. (2011). "Great Canadian Lagerstätten 1. Early Eocene Lagerstätten of the Okanagan Highlands (British Columbia and Washington State)". Geoscience Canada. 38 (4): 155–164.
↑ DeVore, M. L.; Nyandwi, A.; Eckardt, W.; Bizuru, E.; Mujawamariya, M.; Pigg, K. B. (2020). "Urticaceae leaves with stinging trichomes were already present in latest early Eocene Okanogan Highlands, British Columbia, Canada". American Journal of Botany. 107 (10): 1449–1456. doi: 10.1002/ajb2.1548 . PMID 33091153. S2CID 225050834.
1 2 3 4 5 Greenwood, D.R.; Archibald, S.B.; Mathewes, R.W; Moss, P.T. (2005). "Fossil biotas from the Okanagan Highlands, southern British Columbia and northeastern Washington State: climates and ecosystems across an Eocene landscape". Canadian Journal of Earth Sciences. 42 (2): 167–185. Bibcode:2005CaJES..42..167G. doi:10.1139/e04-100.

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[Pigg2021-1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pigg, K. B.; DeVore, M. L.; Greenwood, D. R.; Sundue, M. A.; Schwartsburd, P.; Basinger, J. F. (2021). "Fossil Dennstaedtiaceae and Hymenophyllaceae from the Early Eocene of the Pacific Northwest". International Journal of Plant Sciences. 182 (9): 793–807. doi:10.1086/715633. S2CID 239036762.

[BurAm22-2] 1 2 Li, Y.; Wang, Y.-D.; Nosova, N.; Lu, N.; Xu, Y.-Y. (2022). "Filmy Ferns (Hymenophyllaceae) and Associated Spike-Mosses (Selaginellaceae) from the Mid-Cretaceous Kachin Amber, Myanmar". Biology. 11 (11). 1629. doi: 10.3390/biology11111629 . PMC 9687414 . PMID 36358330.

[3] Li, Y.; Ebihara, A.; Nosova, N.; Tan, Z.-Z.; Cui, Y.-M. (2023). "First Fossil Record of Trichomanessensu lato (Hymenophyllaceae) from the Mid-Cretaceous Kachin Amber, Myanmar". Life. 13 (8). 1709. Bibcode:2023Life...13.1709L. doi: 10.3390/life13081709 . PMC 10455793 . PMID 37629566.

[Mecodium-4] Chang, Z.X.; Hsu, T.C.; Kuo, L.Y. (2022). "Hymenophyllum chamaecyparicola (Hymenophyllaceae), a new filmy fern species from Taiwan". PhytoKeys (23): 23–34. doi: 10.3897/phytokeys.204.86045 . PMC 9848887 . PMID 36760617.

[GCL2011-5] 1 2 3 Archibald, S.; Greenwood, D.; Smith, R.; Mathewes, R.; Basinger, J. (2011). "Great Canadian Lagerstätten 1. Early Eocene Lagerstätten of the Okanagan Highlands (British Columbia and Washington State)". Geoscience Canada. 38 (4): 155–164.

[DeVore2020-6] DeVore, M. L.; Nyandwi, A.; Eckardt, W.; Bizuru, E.; Mujawamariya, M.; Pigg, K. B. (2020). "Urticaceae leaves with stinging trichomes were already present in latest early Eocene Okanogan Highlands, British Columbia, Canada". American Journal of Botany. 107 (10): 1449–1456. doi: 10.1002/ajb2.1548 . PMID 33091153. S2CID 225050834.

[Greenwood2005-7] 1 2 3 4 5 Greenwood, D.R.; Archibald, S.B.; Mathewes, R.W; Moss, P.T. (2005). "Fossil biotas from the Okanagan Highlands, southern British Columbia and northeastern Washington State: climates and ecosystems across an Eocene landscape". Canadian Journal of Earth Sciences. 42 (2): 167–185. Bibcode:2005CaJES..42..167G. doi:10.1139/e04-100.

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