Dawsonia superba

Dawsonia superba is a moss in the class Polytrichaceae that is found in Australia, New Guinea, Malaysia[1] and New Zealand.[2] D. superba is the tallest self-supporting moss in the world, reaching heights of 60 cm (24 in).[3] It has analogous structures to those in vascular plants that support large size, including hydroid and leptoid cells to conduct water and photosynthate,[3] and lamellae that provide gas chambers for more efficient photosynthesis.[4] D. superba is a member of the class Polytrichopsida, although it has a sporophyte that is unique from other hair-cap mosses.[4]

Dawsonia
Dawsonia superba in Abel Tasman National Park, New Zealand
Scientific classification Edit this classification
Kingdom: Plantae
Division: Bryophyta
Class: Polytrichopsida
Order: Polytrichales
Family: Polytrichaceae
Genus: Dawsonia
Species:
D. superba
Binomial name
Dawsonia superba
Grev., 1847

There is some confusion surrounding if Dawsonia superba and Dawsonia longifolia are distinct species or refer to the same moss. According to some sources, Dawsonia longifolia and Dawsonia superba have been merged.[3] For a long time, both D. longifolia and D. superba were used to refer to the same species, with some regional variation in its use.[5] Both terms are still used today.

Distribution and habitat

The species is commonly found in Australia, New Guinea, Malaysia[1] and New Zealand.[2] D. superba prefers “moist, well-illuminated environments”,[4] cloud forests,[4] and shady forests.[6] It has often been observed growing at the base of uprooted trees.[7]

Gametophyte

Like all bryophytes, D. superba has a dominant gametophyte stage. The gametophyte is the haploid stage of the life cycle, and is composed of leaves, a stem, and root-like rhizoids.[3] These rhizoids extend farther underground than is typical of other mosses.[8][9]

A cross section of Dawsonia superba stem. A central conducting hydrome is visible, as well as leptome cells and leaf traces.

The stem of the D. superba gametophyte has a central conducting strand and leaf traces. The stem has hydroid cells that conduct water, and leptoid cells that conduct photosynthate.[3] According to Zanten (1973), the stem of D. superba is also characterized by the presence of sclerenchyma, which are cells with lignin in their cell walls.[10] However, chemical analyses have shown that D. superba does not contain lignin,[11] although it may contain a lignin-like component.[12]  

The leaves of D. superba can be up to 30 mm (1.2 in) long.[13] Like other polytrichid mosses, the leaves of D. superba have lamellae.[3] Lamellae are made up of rows of lamella that are one cell thick and several cells high. These rows of lamella sit atop the leaf’s midrib, or costa. Each cell contains many chloroplasts.[3] Lamellae increase the available surface area of the leaf for photosynthesis, and air spaces between each lamella allow for gas exchange to make photosynthesis more efficient.[4] Lamellae have been referred to as “pseudo-mesophyll”, meaning that they are analogous to mesophyll structures in vascular plant leaves, which also aid in gas exchange.[4] Lamellae allow mosses to tolerate higher light saturation, which allows them to photosynthesis efficiently even in bright light, unlike other mosses with a unistratose leaf.[14]

A waxy cuticle covers the leaf and the top of the lamellae. The wax acts as a hydrophobic barrier, so that air spaces in the lamellae are protected from both drying out and over-saturation from rainwater.[15]

Sporophyte

The diploid sporophyte of D. superba is produced from gametophytic tissue and is dependent on the gametophyte for water and nutrients. A long seta extends the sporangium above the gametophyte. The sporangium is the site of meiosis, and haploid spores are released from the sporangium through the peristome teeth. As in all members of the class Polytrichopsida, D. superba has nematodontous peristome teeth.[3] This means that the peristome teeth are made up of whole cells.[13] However, members of the genus Dawsonia have unique bristle-like peristome teeth. These teeth are arranged circularly in multiple rows and form a brush-like turf that spores are released through. No epiphragms are present in the Dawsoniaceae group.[4]

The spores are dispersed over time from between these peristome teeth. Spores of D. superba are small (7 μm in diameter)[16] and smooth.[13] Once they have germinated, spores form protonemal shoots that develop into gametophytes.[17]

Reproduction

Sexual reproduction

The gametophytes of D. superba are diocious, meaning that the male and female reproductive structures are housed on separate plants. The male reproductive structure, or antheridium, produces sperm that must reach a female archegonial plant in order for fertilization to occur.[3]

While male and female plants are separate in D. superba, they often grow very close to each other. In order to disperse sperm, male gametophytes use what is called a splash-cup mechanism. Archegonia are found at the tips of gametophytic shoots. The leaves surrounding the antheridia, also called perigonial leaves, form a shallow cup-like structure. Water that falls into this cup collects sperm, and as the water splashes out of the cup the sperm is carried out with it. Using this mechanism, sperm can be dispersed up to 3 metres (9.8 ft) away from the male gametophyte.[18]

Asexual reproduction

Leaves, when isolated from the rest of the plant, have been shown by Selkirk (1980) to develop protonemal filaments, although this regeneration is rare in D. superba compared to other members of the genus.[19] Additionally, rhizomes often send up vegetative shoots.[7]

Growth and height
Dried vegetative samples of Dawsonia superba gametophytes.

D. superba is the tallest known moss and can grow up to a height of 60 cm (24 in). Growth rates as high as 48 mm (1.9 in) per year have been observed, although the average growth rate is likely closer to 20 mm (0.79 in) per year. Temperature is the most important factor for growth, with the second most important factor being optimal water levels.[7]

In order to grow tall, a plant must be able to conduct enough photosynthesis to have energy for growth, and have enough water to continue photosynthesis. Therefore, high photosynthetic efficiency and some sort of water transport system is necessary for plants to reach a certain height.[20] D. superba has a hydroid system to conduct water and a leptoid system to conduct photosynthate, which allows the plant to stay hydrated internally. Surface wax on leaves also reduces desiccation.[15] D. superba also has lamellae on its leaves. Lamellae increase photosynthetic surface area and provide spaces for gas exchange, both of which increase photosynthetic efficiency.[4] These traits combined allow D. superba to grow taller than other mosses.

Indigenous use

There are many traditional uses for D. superba, many of which utilize the moss’s size for decoration. Indigenous peoples in New Guinea and Malaysia have used Dawsonia species as decoration. This has ranged from it being worn as headwear, body decoration, decoration of ceremonial masks, bracelets, and bags.[21][22][23][6] Additionally, in Malaysia large mosses such as Dawsonia are thought to ward off evil spirits.[24]

References
  1. Eakin, David A. (1998-09-28). "A taxonomic revision of the moss genus Regmatodon". Nova Hedwigia. 67 (1–2): 139–152. doi:10.1127/nova.hedwigia/67/1998/139. ISSN 0029-5035.
  2. "Dawsonia superba - The University of Auckland". www.nzplants.auckland.ac.nz. Retrieved 2022-04-06.
  3. Glime, Janice M.; Tuba, Zoltan; Slack, Nancy G.; Stark, Lloyd R. (2010), "Ecological and Physiological Effects of Changing Climate on Aquatic Bryophytes", Bryophyte Ecology and Climate Change, Cambridge: Cambridge University Press, pp. 93–114, doi:10.1017/cbo9780511779701.007, ISBN 9780511779701, retrieved 2022-04-06
  4. Bell, Neil; Kariyawasam, Isuru; Flores, Jorge; Hyvönen, Jaakko (2021-06-30). "The diversity of the Polytrichopsida—a review". Bryophyte Diversity and Evolution. 43 (1). doi:10.11646/bde.43.1.8. ISSN 2381-9685. S2CID 237385196.
  5. Zanten, B. O.; Margadant, W. D. (1997). "Proposal to conserve the name Dawsonia superba (Musci, Dawsoniaceae)". Taxon. 46 (3): 547–549. doi:10.2307/1224402. ISSN 0040-0262. JSTOR 1224402.
  6. van Zanten, B. O. (1973). "A Taxonomic Revision of the Genus Dawsonia R. Brown". Lindbergia. 2 (1/2): 1–48. ISSN 0105-0761. JSTOR 20149203.
  7. Green, T. G. A.; Clayton-Greene, K. A. (1981). "Studies on Dawsonia superba Grev. II. Growth rate". Journal of Bryology. 11 (4): 723–731. doi:10.1179/jbr.1981.11.4.723. ISSN 0373-6687.
  8. Proctor, M. C. F. (1982), Smith, A. J. E. (ed.), "Physiological Ecology: Water Relations, Light and Temperature Responses, Carbon Balance", Bryophyte Ecology, Dordrecht: Springer Netherlands, pp. 333–381, doi:10.1007/978-94-009-5891-3_10, ISBN 978-94-009-5891-3, retrieved 2022-04-06
  9. 弘之, 秋山 (2009). "地中深くに伸びるボルネオ産ネジクチスギゴケ属 Dawsonia superbaのシュート地下部について(アジア産蘚苔類の分類・生態ノート,19)". 蘚苔類研究. 9 (12): 391–394. doi:10.24474/bryologicalresearch.9.12_391.
  10. "Sclerenchyma - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2022-04-06.
  11. Miksche, G. E.; Yasuda, S. (1978-01-01). "Lignin of 'giant' mosses and some related species". Phytochemistry. 17 (3): 503–504. doi:10.1016/S0031-9422(00)89348-6. ISSN 0031-9422.
  12. Ligrone, R.; Carafa, A.; Duckett, J. G.; Renzaglia, K. S.; Ruel, K. (2008). "Immunocytochemical detection of lignin-related epitopes in cell walls in bryophytes and the charalean alga Nitella". Plant Systematics and Evolution. 270 (3–4): 257–272. doi:10.1007/s00606-007-0617-z. ISSN 0378-2697. S2CID 24711594.
  13. Gilmore, S.R. (2006). Flora of Australia. Canberra & Melbourne: ABRS and CSIRO Publishing. ISBN 0643092404.
  14. Proctor, M. C. F. (2005). "Why do Polytrichaceae have lamellae?". Journal of Bryology. 27 (3): 221–229. doi:10.1179/174328205X69968. ISSN 0373-6687. S2CID 84580845.
  15. Clayton-Greene, K. A.; Collins, N. J.; Green, T. G. A.; Proctor, M. C. F. (1985). "Surface wax, structure and function in leaves of Polytrichaceae". Journal of Bryology. 13 (4): 549–562. doi:10.1179/jbr.1985.13.4.549. ISSN 0373-6687.
  16. Stetler, D. A.; DeMaggio, A. E. (1976). "Ultrastructural Characteristics of Spore Germination in the Moss Dawsonia Superba". American Journal of Botany. 63 (4): 438–442. doi:10.1002/j.1537-2197.1976.tb11831.x. ISSN 0002-9122.
  17. DeMaggio, A. E.; Stetler, D. A. (1977). "Protonemal Organization and Growth in the Moss Dawsonia Superba: Ultrastructural Characteristics". American Journal of Botany. 64 (4): 449–454. doi:10.1002/j.1537-2197.1977.tb12367.x. ISSN 0002-9122.
  18. Clayton-Greene, K. A.; Green, T. G. A.; Staples, B. (1977). "Studies of Dawsonia superba. 1. Antherozoid Dispersal". The Bryologist. 80 (3): 439. doi:10.2307/3242019. JSTOR 3242019.
  19. McCarthy, John A.; Kurth-Voigt, Lieselotte E. (1976). "Perspectives and Points of View: The Early Works of Wieland and Their Background". The Modern Language Journal. 60 (3): 134. doi:10.2307/324214. JSTOR 324214.
  20. Bok, Erin C. P. M.; Brodribb, Timothy J.; Jordan, Gregory J.; Carriquí, Marc (2021). "Convergent tip‐to‐base widening of water‐conducting conduits in the tallest bryophytes". American Journal of Botany. 109 (2): 322–332. doi:10.1002/ajb2.1795. ISSN 0002-9122. PMID 34713894. S2CID 240154324.
  21. Dickson, James H. (2000), "Bryology and the Iceman: Chorology, Ecology and Ethnobotany of the Mosses Neckera complanata Hedw. and N. crispa Hedw.", The Iceman and his Natural Environment, Vienna: Springer Vienna, pp. 77–87, doi:10.1007/978-3-7091-6758-8_7, ISBN 978-3-7091-7403-6, retrieved 2022-04-06
  22. MCLAUGHLIN, S (2005). "Plant Resources of South-East Asia No. 17: Fibre PlantsM. Brink, R.P. Escobin (Eds.), 2003, Backhuys Publishers, Leiden, The Netherlands, 456 pp., 120, ISBN 90-5782-129-X". Industrial Crops and Products. 21 (3): 391. doi:10.1016/s0926-6690(04)00097-4. ISSN 0926-6690.
  23. Taylor, Hope C.; Richardson, David C.; Richardson, Jane S.; Wlodawer, Alexander; Komoriya, Akira; Chaiken, Irwin M. (1981). ""Active" conformation of an inactive semi-synthetic ribonuclease-S". Journal of Molecular Biology. 149 (2): 313–317. doi:10.1016/0022-2836(81)90305-3. ISSN 0022-2836. PMID 7310884.
  24. "Bryophyte Ecology ebook | Michigan Technological University Research | Digital Commons @ Michigan Tech". digitalcommons.mtu.edu. Retrieved 2022-04-06.
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