Bryophytes of Two Peoples Bay Nature Reserve, Western Australia

Introduction

Study of the bryophyte flora of Western Australia has been limited. According to Ramsay (1977), the flora is thought to be depauperate, with only about 100 species compared with more than 1200 species for the rest of Australia. In The Mosses of Southern Australia, Scott and Stone (1976) listed a total of 102 species documented for Western Australia. A census published in 1993, however, reported nearly twice as many: 192 species in 78 genera and 31 families (Stoneburner et al. 1993). Ramsay (1977) also predicted low levels of endemism in the bryophyte flora, in contrast to the high degree of endemism known among flowering plants (Beard 1981; Gioia and Hopper 2017). Ramsay suggested that the low incidence of rainforest habitat may explain why the bryophyte flora is not rich and diverse. From our own experience in the Southwest Australian Floristic Region (SWAFR, Fig. 1), it appears that this assumed low diversity may be attributed at least in part to a paucity of bryophyte collecting (Stoneburner et al. 1993).

Fig. 1.

Maps of Two Peoples Bay Nature Reserve and (inset) the Southwest Australian Floristic Region showing Provinces and Districts identified by Gioia and Hopper (2017). Collecting localities of bryophytes are in green boxes. These include Robinson Gully (RG); forest at Reserve Office (RO); Waterfall Beach (WB); Sinker Reef (SRf); Rock Island (RI); Sheoak Ridge (SRd); and margins of Lake Gardner (LG). See Tables 1 and 2 for species collected. Base map by A. J. M. Hopkins and G. T. Smith.

On the other hand, it is probably true that endemism is low, as only four species of mosses and liverworts are known to be restricted to Western Australia. Note, however, that most of our collections were made in the SWAFR, which is famous for high levels of diversity and endemism in the vascular flora (Hopper and Gioia 2004; Gioia and Hopper 2017). Recent development of OCBIL (Old, Climatically Buffered, Infertile Landscapes) theory to explain high diversity and endemism in regions like the SWAFR (Hopper 2009, 2023) may not apply to mosses and liverworts, whose tiny spores are highly dispersible and may be carried over long distances. The first of seven predictions derived from OCBIL theory is that organisms should exhibit reduced dispersibility, leading to high numbers of localised rare endemics and strongly differentiated population systems. Along with many other bryologists, Crum (1972) argued that bryophytes can be considered part of the natural assemblage of whole floras acted upon by the same geological, climatic, and ecological conditions that shape the evolution of the vascular members of that flora. Yet, this seems not to apply to the situation in Western Australia.

At Two Peoples Bay Nature Reserve, the moderate Mediterranean climate with wet, mild winters and cool, dry summers (Hopkins et al. 2024) provides favourable conditions for establishment and growth of bryophyte colonies. The relative youth of much of the landmass of the Reserve, however, may have hindered development of a diverse bryophyte flora. However, the Mt Gardner headland has been above the sea for at least 250 million years (Kohn et al. 2002), likely as a nearshore island during high sea levels (González-Álvarez et al. 2016), thus forming a classic OCBIL (Hopper 2009, 2023), whereas with fluctuating Quaternary sea levels the sands of the isthmus and lakes areas have accumulated only since the mid-Pleistocene (P. E. Playford and I. Tyler, unpubl. data). Crum (1972) argued that, for most species of bryophytes, long-distance dispersal is not common. Nevertheless, wind is an important factor in the environment of the Reserve (Hopkins et al. 2024) and may play a larger role here than expected in long-distance dispersal by spores or plant fragments.

Materials and methods

During the period from April to September 1984, seven sites were visited in the Reserve (Fig. 1) and 105 collections of mosses and 19 of liverworts were made. Voucher specimens of all collections were deposited in the Western Australian Herbarium (PERTH) and in the bryophyte herbarium at Duke University (DUKE). Prior to this survey only one specimen from Two Peoples Bay Nature Reserve (Campylopus bicolor from Mt Gardner) had been collected (PERTH). A limited number of collections made after our survey was completed have been reported to us. These reports are included in Table 1 under the heading ‘Other Collections’.

This survey should be considered a preliminary one. An attempt was made to visit different kinds of habitats in the relatively short time available. More time will be required in the future to study in detail mesic habitats, especially the gullies and sclerophyll woodlands.

Mosses were identified using the manuals of Catcheside (1980) and Scott and Stone (1976) and by comparison with specimens from PERTH and the herbarium of the University of Western Australia (UWA, now incorporated at PERTH). Geographical distributions of the species were noted and compared for provinces within Western Australia, using Beard’s (1980) classification, and within Australia and the rest of the world, as described in the aforementioned manuals and Index Muscorum (van der Wijk et al. 1959–1969). These data were then updated to conform to Gioia and Hopper’s (2017) classification of phytogeographic floristic regions, provinces and districts in the SWAFR. Liverworts were identified using keys made available and subsequently published by Scott (1985). Members of the genus Riccardia were identified using Hewson’s (1970) keys and descriptions. For some problematical specimens we enlisted the help of David G. Catcheside, Ilma G. Stone and George A. M. Scott. Using Tropicos, a plant database maintained by the Missouri Botanical Garden that links more than 1.38 million scientific names with more than 6.94 million specimens, the taxonomy and nomenclature of all the mosses were brought up to date. For liverworts we used the 828-page world checklist of hornworts and liverworts published by Söderström et al. (2016).

Results

Discussion

Worldwide there are about 14,000 species of mosses and liverworts. Their origin is thought to be more ancient than that of vascular plants (Bechteler et al. 2023). Except for local colonisations of newly available or disturbed sites, their present distributional patterns probably antedate the origin of flowering plants and the breakup of Gondwanaland in the Cretaceous (Crum 1972). A rich and diverse bryophyte flora would not be expected along that portion of the south-west coast that is of geologically recent exposure except where bedrock persists as elevated OCBIL uplands such as Mt Gardner. The genus to species ratio, 1:1.85, is nearly identical to that of mosses of the Hawaiian Islands (1:1.80), another landmass of geologically recent (though pyroclastic) origin (Crum 1972).

The Pottiaceae, the most common family occurring in the Reserve, constitutes a highly polymorphic group. Many of its members are adapted to semi-arid to arid conditions and are commonly thought of as small, tufted mosses of soil and typically basic rocks. There have been many recent changes in the taxonomy of these plants, including recognition of many new genera, based on modern gene sequencing and phylogenetic reconstructions (Bechteler et al. 2023).

Regardless of family relationships, nearly one-half of the species collected in the Reserve have the capacity to occupy open, relatively dry habitats. The morphological adaptations to drought of several of these species have been described in detail by Scott (1982). Those sites with the greatest diversity and cover of bryophytes are the most mesic, especially Robinson Gully and the sclerophyll forests adjacent to the picnic area near the Reserve Office. The driest sites support a distinctly depauperate bryophyte flora, particularly ‘Rock Island’, the shores of Gardner Lake, and Sheoak Ridge.

The bryophyte flora of the Reserve is, as expected, similar to that of adjacent regions. Only three species (Campylopus pallidus, Pseudocrossidium crinitum, and Funaria microstoma) had not been collected previously from the Muir and Jarrah Districts, although they are known from other districts in the SWAFR. Most of the other collections from Two Peoples Bay Nature Reserve represent species that have also been reported from the Muir and Jarrah Districts. The Southeast Coastal Floristic Province appears to have a decidedly lesser overlap with the flora, and the Kalbarri Floristic Province and Boylya Floristic District have the least.

Some distinctive differences in substrate preferences can be identified based on our collections and field experience. Species found primarily on granite rocks, presumed to be acidic, include C. bicolor, Dicranoloma diaphanoneuron, P. occidentale, Rhacocarpus purpurascens, and S. homomallum. P. occidentale has, however, been found on a range of other substrates including quartzite, spongelite and laterite subsequent to our work reported herein. On limestone rocks and soils derived therefrom, presumed to be basic, the following are commonly found: Didymodon australasiae, Gymnostomum calcareum, Funaria salsicola, Tortella rubripes, and Trichostomum eckelianum. An oddity on display near the Reserve Office of Two Peoples Bay is a partial skeleton of a ‘100-year-old right whale’ (Eubalaena australis). The cranium and some of the vertebrae supported growth of several mosses including Barbula calycina, Bryum chrysoneuron, Codonoblepharum menziesii, D. australasiae, Syntrichia princeps, and Thuidium laeviusculum. All of these appear to be species that prefer basic substrates (e.g. Duckett 2017), and recent study of blue (Balaenoptera musculus) and humpback (Megaptera novaeangliae) whale skeletons from Antarctica showed the pH ranges from 7.50 to 8.10 (Putzke et al. 2022).

The flora of south-west Western Australia and South Australia appear very similar, thereby making Mosses of South Australia (Catcheside 1980) an invaluable manual for collectors in Western Australia. Species collected at five or more sites show the following geographical affinities: Racopilum cuspidigerum (Fig. 2) is endemic to Australia and New Zealand; B. calycina and C. bicolor show a Gondwanaland distribution; Campylopus introflexus is cosmopolitan; and S. homomallum (Figs 3 and 4) is found in Australia, New Zealand, and parts of Asia.

Fig. 2.

Racopilum cuspidigerum, one of the most common mosses from Two Peoples Bay Nature Reserve, was collected from five sites. Photo taken in Porongurup, WA. Except as noted, all photos are courtesy of iNaturalist and used under the Creative Commons Attribution-Non-Commercial (CC BY-NC) license.

Fig. 3.

Sematophyllum homomallum is very common on acidic rocks, logs, and bases of trees and was collected from six sites in Two Peoples Bay Nature Reserve. Photo taken in Hazelvale, WA.

Fig. 4.

Sematophyllum homomallum showing its distinctive red and gold colour, though new growth is often green. Photo taken in Denmark, WA.

Although the majority of species collected from the Reserve were not unexpected, several collections support the importance of continuing the bryophyte survey: D. inclinatum and T. dakinii had not been reported previously from Western Australia, and initially three species appeared to be new to science. Two of these taxa belonged to genera which are notorious for blurred species boundaries (Bryum and Tortella). With further study these taxa have been assigned to Rosulabryum subtomentosum and T. eckelianum. P. occidentale (Figs 5 and 6), however, differs distinctly from the one described species of the genus, Pleurophascum grandiglobum (Fig. 6), and represents a striking geographical disjunction of the genus from Tasmania and New Zealand, where the latter occurs (Wyatt and Stoneburner 1989). The new species differs in numerous characters from P. grandiglobum, described by Scott and Stone (1976) as a ‘famous bryological rarity’. It is a much larger plant overall with leaves 6 mm × 2.5 mm vs 2–3 mm × 1 mm, a flexuose, hoary, serrate vs rounded to bluntly obtuse leaf tip, and nearly sessile, large, orange, obovoid capsules vs longer-stalked, smaller, and lighter-coloured capsules (Figs 5 and 6). Since our original collection, searching west and east of Two Peoples Bay has significantly extended the range of the species (Fig. 6d). Clearly, it is important to continue floristic investigations of mosses in the SWAFR, a region unique in its geographical diversity and ecological amplitude. More thorough sampling of different habitats and substrates will undoubtedly add many new species of mosses and liverworts to the list of species in the region.

Fig. 5.

Pleurophascum occidentale with its large, orange, obovoid capsules on very short setae. North-east of Esperance. Photo Michael Warren, iNaturalist.

Fig. 6.

Pleurophascum grandiglobum immersed in water in situ in Tasmania: (a) photo M. Brown, (b) photo David Tng. Pleurophascum occidentale north-east of Esperance: (c) photo Michael Warren iNaturalist. (d) Pleurophascum occidentale distribution (blue markers) from Florabase February 2024. Pleurophascum occidentale was a new species in a previously monotypic genus and family when first collected and described from Two Peoples Bay Nature Reserve. Its range is now known to extend east to the Esperance district, WA.

The hepatic flora of Australia is even less well-studied than the moss flora. Scott’s (1985) manual has done much to remedy that situation for southern Australia, though he does not consider his manual exhaustive in scope. Distributional information available for Australian liverworts is especially incomplete. The list of species reported here should not be considered definitive, but rather an indication of the orders, families, and genera likely to be most common in the Reserve. Both thalloid (Riccardia crassa: Fig. 7) and leafy (Lophocolea semiteres: Fig. 8) growth forms are represented. For southern Australia, Scott (1985) lists 80 genera in 33 families and five orders.

Fig. 7.

Riccardia crassa, an impressive thalloid liverwort that grows on streambanks, was collected from two sites in Two Peoples Bay Nature Reserve. Photo taken in Walpole, WA.

Fig. 8.

Lophocolea semiteres is a leafy liverwort, often growing on bark at the base of Eucalyptus trees, collected from three sites in Two Peoples Bay Nature Reserve. Photo taken in Albany, WA.

Bryophytes play an important role in soil conservation (Moul and Buell 1955; Golding and Stanton 1972), vegetation development (Thieret 1956), and nutrient cycling (Brown 1982). A well-developed colony of a moss or liverwort may be decades in the making. It is well to remember ‘that mosses are vulnerable … and that indiscriminate or wasteful collecting is unethical, immoral and altogether to be deplored’ (Scott and Stone 1976). Of even greater concern in terms of preserving the bryophyte flora is prevention of careless four-wheel driving and use of trail bikes and mountain bikes on granite outcrops and other sensitive habitats that support large colonies of mosses and liverworts (Fig. 9) Research on repair and restoration of such needless destruction of moss mats due to trail damage is only just beginning (e.g. Medeiros et al. 2023). Management policy at Two Peoples Bay Nature Reserve should continue with protection of the flora and fauna as its number one priority.

Fig. 9.

Granite outcrop moss mats are particularly susceptible to erosion through off road vehicle use such as by mountain bikes, trail bikes, quad bikes and 4WD vehicles. Moss mats often provide habitat for threatened geophytes and annual plants, as well as resurrection plants such as Borya nitida (a). Photos by S.D. Hopper of damage caused to moss mats by: (a) mountain bikes at Mt Clarence Albany; (b) 4WD vehicles at Blue Rock SE of Perth; (c) pedestrian trail Mt Chudulup; (d) trail bikes at Blue Rock; (e) 4WD vehicles and trail bikes at Wandoo National Park east of Perth viewed by participants at a granite rock conservation conference.