Cyathea
Genus Cyathea (Smith, J.E. 1793) (470-600 species), is by far the largest of a small number of genera constituting the family Cyatheaceae. It comprises mainly terrestrial tree ferns, most often presenting with a single tall stem, but rarely the trunk may be creeping or branched. Many species develop a tangled mass of roots at the base of the trunk. The fronds range in size from 0.25 m to 6 m (usually 2-4 m). The genus is distributed predominantly in the New World (Caribbean to South America), but the subgenus (also Cyathea) extends across the pacific to Australia. Habitats range from tropical lowland rain forest to the Andes mountains (4200 m). (Braggins & Large,2004).
Genus not rare or threatened, but is alien to Western Australia (Flora Base of Western Australia)
The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>.
Downloaded on 04 October 2014. 13 species listed (NONE IN AUSTRALIA)
Genus not rare or threatened, but is alien to Western Australia (Flora Base of Western Australia)
The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>.
Downloaded on 04 October 2014. 13 species listed (NONE IN AUSTRALIA)
Tree ferns or large terrestrial ferns with usually erect woody trunks, rarely growing on rainforest trees. Vascular tissue is of the meristele variety. The trunk base is often covered with interwoven lateral roots. Stems have their bases or entire length covered with scales, short, stiff hairs being present on the inner (adaxial) stem surface, the outer (abaxial) surface bearing discontinuous lines of small air holes (pneumathodes). The leaf blades (pinnae), each of which have a small pneumathode at their base, are commonly bi or tripinnate, rarely pinnate, dividing into small leaflets (pinnules). The lower pinnae are smaller, never having elongate pinnules. The rachis has a hairy adaxial surface, with a rarely hairy, but variously scaly abaxial surface. Scales become progressively smaller distally and on the central stem (costae) of pinnules, the latter of which are variously lobed pinnate. Veins are mostly simple or forked, and are pinnate in pinnule lobes, being free to the margin. Sori, with or without indusia, are found on or near veins. Indusia of varying size are either attached all around, covering the young sorus and forming a cup, or attached only on their costal aspect. In some cases the indusium may be hidden by a mature sorus. Species lacking indusia may have overlapping scales either covered by, or to varying degrees, covering the sporangia. The sporangia are almost sessile, being narrower towards the base, and displaying a complete oblique annulus. Spores are trilete (four spores conjoined), and clustered in groups of 4, 16, 32, or 64 per sporangium. (Kramer, K. U., & Green, P.S. (1990). Cyatheaceae, Fam. & Gen. Vascular Pl. 1, 71-72.)
Photosynthesis: It has been known for some time that rates of photosynthesis in ferns is somewhat lower than in seed plants. Little is known with respect to the aetiology of such limitations. A representative range of ferns were tested for a number of factors including maximum net photosynthesis (An), stomatal CO2 conductance (Gs) and mesophyll CO2 conductance (Gm), and the maximum velocity of carboxylation (Vc). All four parameters were measured to be within the lowest range of those observed in seed plants. In addition, Gs was unresponsive to light and CO2. However, Gm varied with changes in CO2. Although not completely understood, these data suggest that early plants (ferns) possessed a combination of limiting processes, mainly stomatal, due to the absence of well defined companion cells as seen in seed plants, resulting in ferns exhibitilng high stomatal turgor senssitivity. This combined with ferns intrinsic low water and nitrogen use efficiency, results in an overall low photosynthetic efficiency when compared to seed plants. (Gago et al. 2013).
Molecular DNA analysis of the three genome compartments (nuclear, plastid and mitochrondrial) of ferns, has revealed a link between the origin of arborescence and the rate of molecular evolution. Reference to the phylogenetic tree shows that branch lengths within the ‘tree fern’ clade are substantially shorter than those of neighbouring closely related lineages; heterosporous ferns and the polypods. Approximately 190 mya saw the beginnings of the ‘tree’(arborescent) ferns, coinciding with which was an abrupt deceleration of their molecular evolutionary rate (19% the rate of heterosporous ferns, and 15% that of polypods). It is known that the tree ferns are long-lived, and consequent to this, have an inherently slow rate of molecular evolution.This implies that over any given time period, a smaller number of DNA mutations occur when compared to more short-lived species. The short phylogenetic branch lengths of the tree ferns therefore signify less evolutionary change. Studies have shown that the molecular evolutionary rates of arborescent species are markedly lower than their herbaceous counterparts. Results of this study strongly suggest that there is an inverse relationship between molecular evolutionary rate and generation time; as one goes up, the other goes down. It is perplexing why this should be so, and further work will hopefully elucidate contributing metabolic processes.
One hypothesis is related to the alternations of generations seen in land plants. Arborescent species are known to have an exceptionally long sporophytic stage, whereas the gametophytic stage is comparable to herbaceous plants. It is thought that perhaps these two developmental stages are differentially susceptible to mutational change. If, for example, the gametophyte was more prone to mutation than the sporophyte, then arborescent taxa such as tree ferns, could conceivably display slowed rates of molecular evolution. (Korall et al, 2010)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This study attempts to explain the present biogeography of Cyatheaceae, establishing a correlation between its global distribution and the geological breakup of ‘Gondwanan’ (the early conjoining of South America and Australasia), together with some limited transoceanic dispersal events. This breaking apart of the continents is known as ‘Vicariance’. These evolutionary events are relevant to the genus Cyathea, it being, for all intents and purposes the major genus of the family Cyatheaceae.
This clade is believed to have originated 96 mya, in the mid-Cretaceous, in either Australasia or South America. The crown group of the ‘marginate-scaled’ clade followed a short time later, 83 mya in the late Cretaceous. Cyathea originated thereafter, around 56 mya, at the Palaeocene-Eocene boundary. The vicariance scenario alluded to previously, whereby a basal split occurred in Cyathea, is thought to have occurred between 82 and 54 mya, in the late Cretaceous-Palaeocene. The combination of the continental split and the subsequent ‘range expansion’ effects of spore dispersal, resulted in the present biogeography of the scaly tree ferns. These results are in strong agreement with previous workers (Korall et al, 2007).
Kingdom – Plantae
Phylum – Pteridophyta
Class – Pteridopsida
Order – Cytheales
Family – Cyatheaceae
Genus – Cyathea
Cyathea is the largest of only eight genera within the family Cyatheaceae (Marchant et al, 1987). For this reason, the characteristics of both the family and genus are similar.
Taxonomic analysis, especially with ferns, has always been difficult and time consuming. Historically, the principal rationale for placing organisms into one group was that of morphological similarity, but accurate placement of many genera prior to the introduction of powerful molecular phylogenetic techniques was controversial (Christenhusz & Chase, 2014; Schuettpelz & Pryer, 2008; Preyer et al, 2004). In recent years, these techniques, involving analysis of three genetic compartments, nuclear, plastid and mitochondrial (Preyer et al, 2004), have revolutionized the way in which ferns are being classified. It is increasingly apparent that morphological and genetic similarity often bear a poor correlation with one another. Taxonomists are now faced with a dilemma: should ferns with superficially similar morphology be grouped, or conversely, should those with similar DNA be placed together? Contemporary approaches are based on taking a sort of ‘middle road’ between these two extremes. This so called ‘consensus classification’ (Christenhusz & Chase, 2014) has led to a ‘reshuffling’ of familial and generic inter-relationships, resulting in a reduction in the number of genera in Cyatheaceae. As a consequence, these fewer genera (including Cyathea) have been expanded.
There is general consensus, that in the Devonian (400 mya) a deep split occurred within the Euphyllophytes (Preyer et al, 2004), separating the seed plants (96% of the Euphylls) from the ferns (Schuettpelz & Pryer, 2008). The ferns then evolved into the Leptosporangiates (Carboniferous 360 mya), with greater than 11,000 species, and hence into the ‘core’ Leptosporangiates (Permean 270 mya). Despite the lack of obvious synapomorphies in many tree ferns (Schuettpelz & Pryer, 2008), contemporary molecular analyses gives strong support to both tree ferns and the Leptosporangia as being monophyletic (Schuettpelz & Pryer, 2008; Preyer et al, 2004).
Cyatheaceae is now considered to be equivalent to the ‘scaly tree fern’ clade, and its main genus, Cyathea, as one of four sub-clades (Schuettpelz & Pryer, 2008). Still more study of the tree ferns is critical to further clarify their relationships.[ Ref. Phylogenetic tree (images)]
The genus, consisting of greater than 470 species, is distributed globally in warm to tropical climatic zones. (http://eol.org/data_objects/27559690)
A large group of ancient or primitive land plants with worldwide distribution. Found on all continents except Antarctica and most islands, favouring moist temperate and tropical regions, they can be found in all but the most frigid and most arid environments. Free water is required for fertilization and the production of a new generation of plants. There are no marine species.
(http://www.anbg.gov.au/fern/taxa/pteridophyte.html)
Recent research has shown that certain Cyathera species synthesize flavonoids and their glycosides. In particular, it has been shown that an extract from Cyathera phalerata, known as kaempferol 3-O-neohesperidoside, has insulin-like properties. This substance increases the glucose uptake in cells, thereby reducing blood glucose levels. This so called "insulin mimetic" substance appears to have good potential as a anti diabetes pharmacological agent. (Yamasaki et al. 2011)
Recent comments