About SpiKey
SpiKey: An interactive key to Triodia spinifex grasses of the Pilbara, Western Australia is an interactive identification tool to of the hummock grasses colloquially known as ‘spinifex’ that occur in the Pilbara bioregion and adjacent areas of Western Australia. Hummock grasses belong to the genus Triodia in the family Poaceae. This key covers all 28 species and one hybrid occurring in the region, about one-quarter of the genus, using 28 features. It is intended for use by land managers, botanical consultants, seed collectors, identification botanists and anyone curious about Triodia.
The genus Triodia
Hummock grasses of the genus Triodia are infamously spiky grasses of the Australian arid and semi-arid zones. They are usually referred to as ‘spinifex’ but are only distantly related to coastal grasses of the genus Spinifex. The term hummock grass is often used for Triodia in preference to avoid confusion.
The genus Triodia is endemic to Australia and are structurally and ecologically dominant in the hummock grasslands that cover about 18% of the continent (Anon 2007); they are a dominant understory in other vegetation types over about another 10%. Although they are iconic desert grasses, relatively few species occur in deserts proper. The highest diversity of species is found in rocky areas of seasonally dry savannas of the Pilbara, Kimberley and Northern Territory.
Triodia grasses were important plants for indigenous Australians, providing shelter, edible seed, and a prized resin that could be molded into a thermoplastic polymer and used as an adhesive putty (Gamage et al. 2012). Some species are palatable to stock when young or flowering: a few species are important pastoral fodder (Burbidge, 1946a), while others are considered nothing more than a painful nuisance. More recently, Triodia have been used for building materials and high-quality fibres (Gamage et al. 2014, Amiralian et al. 2015).
Triodia species are important for many arid zone rehabilitation projects, with an associated seed collection industry. Hummock grasslands coincide with many of Australia’s largest mineral resource extraction operations, and consequently are primary targets for rehabilitation of waste rock dumps and other disturbed areas. The Pilbara Seed Atlas (Erickson et al., 2016a) provides an easily accessible guide to Pilbara seed management, including Triodia. More detailed investigations of Triodia restoration and rehabilitation issues and practices can be found in Erickson et al. (2016b), Guzzomi et al. (2016), Lewandrowski et al. (2017), Muñoz-Rojas et al. (2016) and Shackelford et al. (2017).
Why is a new key needed?
Three taxonomic treatments already exist for Triodia: the revisionary work of Lazarides (1997), the treatment for Flora of Australia (Lazarides et al. 2005), and the interactive identification key AusGrass (Sharp & Simon, 2002; updated edition Ausgrass2 available online, Simon & Alonso, 2014). All of these works are primarily based on Lazarides’ original 1997 paper, with few any changes to descriptions.
Since these treatments, much additional survey work in north-western Australia has uncovered variants outside the typical morphological range of species variation. Some of these make the use of existing keys problematic. Genetic and morphometric studies have probed species boundaries in complex species-groups, resulting in new names and changes to the circumscription of some previous species. Molecular phylogenetic research has also improved our understanding of the evolution of key character in Triodia, and allowed a reassessment of the taxonomic importance of some features, particularly leaf anatomy. Detailed studies focusing on the Pilbara bioregion have also resulted in changes to species distributions to those presented in previous treatments.
In addition, the growing importance of Triodia species in minesite and other revegetation projects, and the necessity to accurately identify plants, in the face of this taxonomic complexity, during environmental surveys or when collecting seeds for rehabilitation, has made it timely to produce a new key, especially for the Pilbara region.
SpiKey provides an updated tool accommodating much new information. Species descriptions in the references above should be treated with caution due to changes in circumscription. The extent to which circumscriptions have altered in SpiKey compared to previous work is indicated under the Notes section in each species profile.
Geographic coverage
The area covered by this key is divided into bioregions and sub-regions (outlines in grey, with names in capitals). Towns (black squares) and roads (red) are indicated for orientation.
SpiKey covers a 950 x 500 km area of north-western Australia, between 19° 30’ and 24° 30’ south, and between 113° and 122° 30 east, comprising the Pilbara IBRA7 bioregion (Interim Biogeographic Regionalisation for Australia; DEE, 2007) and surrounds. The IBRA7 bioregions adjacent to the Pilbara (Carnarvon, Great Sandy Desert, Little Sandy Desert and Gascoyne) are partially covered.
Taxonomic coverage
This key covers all known species of Triodia that occur within the area outlined above, centred on the Pilbara.
At the start of 2017 there were 73 accepted and named species of Triodia (Lazarides 1997; Barrett et al. 2005; Armstrong 2008; Hurry et al. 2012; Barrett and Barrett 2011, 2015; Crisp et al. 2015). Recent taxonomic studies suggest Triodia may comprise c. 120 species, including thirteen recently-named species (Anderson et al., 2017a; Barrett, 2017a, b; Barrett & Trudgen, 2017) and many additional known but yet-unnamed species. Recent taxonomic revision have added twelve new species to the Pilbara flora since 2015. SpiKey provides a tool to identify these new Pilbara taxa, and discriminate them from previously described species. Of the 28 species included in this key, 26 occur in the Pilbara bioregion, while three species only in adjacent bioregions; the one hybrid treated is known only from the Pilbara.
Some species names were still unpublished at time of release of version 1 of SpiKey, but have been submitted for publication (early 2017). It is not intended to publish or validate any these names in SpiKey, and hence these names are referred to ined. (ineditus — unpublished and not yet validated), with a reference to their place of intended publication.
Subtle and variable characters have confounded the taxonomy of some groups of Triodia. Genetic data have been used where possible (e.g. Anderson et al. 2016, 2017a, 2017b for the T. basedowii complex) to validate the taxonomy applied here, and extensive DNA ‘barcoding’ has been applied to confirm species distributions, and to confirm the identity of morphological variants.
Taxonomic work is ongoing, with outstanding questions around the identity of the Pilbara form of Triodia “pungens” and its relationship to Triodia epactia, as well as the complex of species around Triodia bitextura. The complex morphological variation included within some Pilbara species remains to be evaluated using genetic markers, particularly in T. angusta, T. brizoides and T. longiceps, but in these cases current species limits are likely to remain.
Challenges when identifying Triodia
Some Triodia species are notoriously difficult to identify reliably. Features that distinguish species are few and plants may vary within and between populations, and with age, fertility and drought stress. Reliable differences between species can sometimes be less than the variation within species, and boundaries between some species are obscure. Further, while florets possess important features for identification, they detach as soon as seeds are set and matured, leaving behind only sterile glumes. Critical features can therefore be easily overlooked, misinterpreted, or may be entirely missing.
This key aims to provide an improved identification guide to the Pilbara Triodia species, focusing on the most reliable features. However, identification can only be as good as the material available, and is greatly facilitated by field observation and careful field observation and collection. Comparative examination of young and old growth, and from multiple plants will greatly assist identification. Increased experience of Triodia species and their features will also improve your collecting and identification.
Hybrid and polyploid complications
A factor driving variation in many grasses is the existence of hybrids and polyploid races. Very few hybrids between Triodia species have been detected to date. Anderson et al. (2016, 2017a, b) noted hybrid swarms between T. chichesterensis and T. lanigera at one location where they co-occur, but did not find evidence of hybridisation at other locations. An isolated population of T. vanleeuwenii at Coondiner Pool in the Fortescue Valley shows some evidence of past introgression with T. scintillans. All of these hybrids are between taxa in the T. basedowii group: such hybrids are not included in the key since they are extremely difficult to discriminate, and require genetic analysis for confirmation.
A rare allopolyploid hybrid (see below) between Triodia longiceps and T. wiseana is included in the key, since it has features that differ consistently from both its parents. Triodia longiceps and T. wiseana co-occur at many locations across the Pilbara, but hybrids are apparently extremely rare; polyploidy (see below) in at least one parental population may be a pre-requisite for formation of the hybrid.
Polyploidy is the result of cellular processes that duplicates chromosomes without cell division, resulting in individuals with twice or more of the normal chromosomal complement. Polyploidy is especially common in grasses. Two types polyploid can be distinguished by differences in gene composition. Autopolyploids result from duplication followed by mating between two individuals of the same species; autopolyploids usually look similar to their parents. Allopolyploids, by contrast, result from duplication and hybridisation between individuals of two separate species; allopolyploids usually look different from (often intermediate between) both parents. One allopolyploid is treated in SpiKey, T. longiceps X wiseana, which is morphologically intermediate between its parents.
Although under-studied, polyploid races are known to exist within many species of Triodia, especially T. brizoides, T. epactia, T. lanigera, T. longiceps, T. pungens and T. wiseana. All known polyploid races within a single species of Triodia have are indistinguishable morphologically, and so they are not discussed further in SpiKey. However, the ploidy levels do tend to segregate into discrete populations, and ploidy may be an important factor for some applications, especially seed sourcing. The most effective method to screen for them is flow cytometry (Barrett et al., in prep.), but geography may allow precise prediction once mapping of these polyploid races is complete across the Pilbara.
