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This species is distinguished from other dioecious Australian solanums by its slender leaves, fine (or absent) armature, and diminutive habit.
TYPE: AUSTRALIA. The Northern Territory: Macadam Range, 14°41'07"S, 129°44'39"E, 15 June 2007 (staminate and pistillate flowers; fruit), Kym G. Brennan 7274 (holotype: DNA! [D0182846]; isotype: PERTH).
Clonal, erect subshrub to 80 cm. Single woody stems 4–5 mm diameter from slender, scarcely-rooted underground stolons, splitting at ca. 40 cm into 2–6 branches. Overall plant aspect yellow-green to gray-green (becoming slightly red-tinged), with older stems eventually woody and gray. Stems with short, dense indumentum of stellate trichomes. Prickles straight, even throughout or slightly widened at base, fine, 5–12mm long, scattered or absent on stems, rarely dense, tending to be absent on woody growth, except near base. Leaves 4–9 cm × 5–10 (-22) mm (largest on newer resprout growth), alternate, linear – lanceolate; margins entire to wavy or rarely lobed; the base tapering to a short petiole 1–1.5 mm long, apex acute; dark green above, slightly lighter beneath, both sides slightly scabrous with short, dense trichomes; trichomes mostly short stalked, porrect-stellate with short central ray. Flowers borne on new growth. Male inflorescence a cyme to at least 6 cm long with 9–12 flowers that are shed successively, only 1–2 flowers open at a time; pedicel 5–7 mm, unarmed; calyx 7 mm long with or without a few prickles towards the base, the lobes ending with a slender filiform acumen ca. 3 mm long; petals 5, fused; corolla 1 cm long, purple, broadly stellate to rotate, acumens 0.5 mm; stamens 5, anthers 2–5 mm long, oblong-lanceolate to somewhat tapered, poricidal, filaments 2 mm; in a loose anther cone; ovary, style, and stigma vestigial and not exserted beyond the stamens. Morphologically hermaphrodite flowers solitary, functionally female with anthers producing inaperturate pollen (Fig. 1F). Female flower on short pedicel; calyx ca. 5 mm, densely armed with long, straight prickles and stellate trichomes; lobes 6 mm, unequal and linear, prickly; corolla ca. 2 cm diameter, 2 cm long, stellate-funnelform, purple; acumens ca. 2 mm; ovary glabrous, 1 mm diameter at anthesis; style erect, 10 mm (including stigmatic surfaces); bifid stigmas 1.5 mm long; stamens of same proportions as in staminate flowers. Peduncle 1.5 cm long, 1.5 mm diameter, sparsely armed with small prickles to 2 mm long. Fruit a green berry 1.2–1.5 cm diameter, globular, drying to black-green and apparently detaching and falling from calyx. Fruiting calyx 2 cm wide, 1.5 cm long, densely armed along sutures, prickles widened (0.5–1 mm) at base and 5–7 mm long, tapering to long fine tip; calyx short stellate-pubescent, more so on sutures and around bases of prickles; calyx lobes extending to slender filiform acumen 5–7 mm long, covered in fine stellate trichomes at tip of each lobe; expanding and surrounding fruit except for ca. 1.5 cm opening at mouth. Calyx retained on stem following fruit drop, at times remaining on plant into next season. Seeds 1.5–2 mm, brown, conspicuously and minutely reticulate.
Distribution and ecology
Solanum cowiei is presently known from a handful of localities in the sub-arid tropical zone of the Northern Territory (a region known colloquially as the “Top End”), most of these habitats are classified under the Tropical eucalypt woodlands/grasslands Major Vegetation Group (National Land and Water Resources 2002). The species is associated with low sandstone outcrops and open eucalypt woodlands, where it typically grows among small boulders or in sandy grassy areas between or around rock formations. The areas where Solanum cowiei has been collected are fire-prone and burn at semi-regular intervals (Fig. 2A, B), allowing for this taxon to compete effectively with species of lesser fire tolerance. While the specific pollination biology is unknown, the flowers are clearly buzz pollinated and are likely visited by bees in the genera Xylocopa and Amegilla, among others (Anderson and Symon 1988). Seed dispersal seems, by initial impressions, to be mechanical. Fruits appear to detach upon maturation, leaving the calyces behind on the plant.
Most flowering specimens have been collected from October-November and March-May, with fruiting specimens collected in Jan-Feb and May. Blooming appears to occur on new shoots soon after burns, as evidenced by dozens of male plants found to be in bud within weeks of managed burns set in the Lost City area of Litchfield National Park in late May, 2013.
Solanum cowiei is named for Dr. Ian Cowie, Chief Botanist at the Northern Territory Herbarium (DNA) and one of the first to recognize the distinct nature of the taxon.
Preliminary conservation status
Based on IUCN Red List Categories (IUCN 2011), Solanum cowiei is considered Data Deficient (DD). The species is relatively widespread, occurring over a geographic range of over 800 km, but it has been collected in fewer than 10 localities. The small number of collections, coupled with the fact that populations outside of Litchfield National Park were only confirmed within the last several years, suggest that the species is common in some localities but uncommon on the regional and global scales. The clonal nature of the species is worth considering, as “populations” of Solanum cowiei often appear to be large multi-stemmed genets connected by an underground network of stolons. Because the species is dioecious, individual genets cannot self-fertilize, leading to the potential for reproductively isolated clonal individuals. Further data are required before a certain conservation status can be determined. Key populations are protected in Litchfield, Limmen and Keep River National Parks and appear secure given current fire management regimes.
AUSTRALIA. Northern Territory: Bullo River Station, 15°35'22"S, 129°29'11"E, 7 May 2008 (fl), I.D. Cowie 12068 (DNA); Bullo River Station, 15°40'14"S, 129°37'31"E, 11 May 2008 (fl), J.O. Westaway 2653 (DNA, NSW); Bullo River Station, 15°39'31"S, 129°34'57"E, 9 May 2008, I.D. Cowie 12095 (DNA, DREF); Bullo River Station, ca. 25 km NW of homestead, 15°16'15"S, 129°47'23"E, 22 March 2009, D.L. Lewis 1192 (DNA, AD); Litchfield National Park, Lost City, 13°13.137’S, 130°44.216’E, 26 May 2009 (fr), C.T. Martine 1753 (DNA, BUPL); Litchfield National Park, Lost City, 13°12'50"S, 130°44'43"E, 8 March 2006 (fr), J.L. Egan & D. Lucas 5716 (DNA); Litchfield National Park at turnoff to Florence Falls, 13°07’S, 130°48’E, 23 November 1990 (fl), I.D. Cowie 1428 & C.R. Dunlop (DNA); Litchfield National Park opposite Florence Falls Rd. turnoff, 13°07'38"S, 130°48'20"E, 20 January 2005 (fl), J.L. Egan s.n. (DNA, AD); 2 km south of Fitzmaurice River Narrows, 14°49'19"S, 129°58'42"E, 14 May 1994 (fl), I. D. Cowie 5030 & D.E. Albrecht (DNA, MEL); Fitzmaurice River, 14°47'28"S, 130°01'04"E, 14 May 1994 (fl), M.J.A. Barritt 1396 (DNA); Bradshaw Field Training Area, ca. 94 km NW of Timber Creek, 15°02'35"S, 129°52'03"E, 4 April 2007 (st), B.M. Stuckey & I.D. Cowie 106 (DNA); Keep River National Park, Spirit Hills area, ca. 27 km NW of Bulloo River Homestead, 15°18'38"S, 129°34'12"E, 18 April 2007 (fr), I.D. Cowie 11692 (DNA, AD); Macadam Range, S of Port Keats, 14°44'00"S, 129°44'00"E, 16 June 2007 (fl), J.O. Westaway 2368 (DNA); Limmen State Park, St. Vidgeons block, 65 km from ruins, 15°16'46"S, 134°31'03"E, 20 April 2009 (st), D.L. Lewis 1160 (DNA).
Solanum cowiei has been known for some time as a local morphotype, having been described by Cowie as Solanum sp. Litchfield as early as 2007. In Litchfield National Park, perhaps the most visited recreation area in the Northern Territory, three primary populations are on routes well travelled by day visitors and campers. The most collected population sits along the road to Florence Falls, with tour buses and cars passing on macadam nearly every day within 10 m of individual plants. Thanks to a series of biodiversity surveys undertaken by staff of the NT Herbarium over the last decade or so (e.g., Cowie et al. 2011, Lewis et al. 2010), the species is now known to have a broader distribution spanning from one side of the Top End from Limmen National Park near the Gulf of Carpenteria in the east to Keep River National Park and northward into the Macadam Range in the west. Across this range many characters remain constant, with leaf lobing (unlobed to slightly lobed) and density of prickles (absent to rarely dense) tending to vary the most.
Vigorous post-fire regrowth has been noted in some areas of deep sand beneath open canopies, with one apparently clonal population in a ca. 20 × 20 m area around the Lost City consisting of ca. 40 ramets (Martine, Evans and Dugan pers. obs.). Resprout growth in this grouping was vigorous and well-armed (Fig. 2C), with numerous male flower buds produced on ramets 12–15 cm tall. While other species in this burn area had also begun to resprout, most had not yet developed flower buds – leading one to believe that the flowers of Solanum cowiei, once opened, would face little local competition for pollinators. While fire is thought to influence the life histories of other species in the Dioicum Complex (Symon 1980), little data exist on its direct effects on recruitment patterns.
Previous molecular work (Martine et al. 2011) reveals that Solanum cowiei is a lineage within the Dioicum Complex – but its relationship to other species in the complex remains unresolved pending continued work in the group (CTM, in progress). Based on morphology, the species appears closely allied to Solanum dioicum and Solanum carduiforme, the latter species also collected during the Limmen and Keep River surveys. On sight, it differs most from Solanum carduiforme in its leaf shape, lobing, and overall growth form. The leaves of Solanum carduiforme are wider (5 cm across), “long-triangular” in shape, with well-developed lobes. Compared to all other solanums in the complex, Solanum cowiei is rather slight of habit, rarely getting taller than knee height and having poorly developed branching. Aerial shoots, while becoming weakly woody, are much like temporary structures, dying back to the underground stolons during fire or when outcompeted during gaps in the fire cycle – only to spring back to life soon after fires have burned.
In support of its disturbance-adapted nature, much of the biomass in populations of Solanum cowiei appears to be below-ground. Stolons function in vegetative reproduction (Fig. 2D), but are also likely important for short-term energy and water storage in the sandy soils inhabited by the species. Stolons unearthed in the field snapped crisply and bore the smell of potato starch. Root systems extending from these stolons are coarse and poorly developed.
The link of this species to fire may be the key determinant of the success of the species in individual sites. In unburned sites surveyed by the first author in the Lost City area of Litchfield National Park (in 2009 and 2013) (Fig. 2A), individual plants were difficult to locate and devoid of reproductive structures. In recently burned areas (Fig. 2B) plants were locally abundant, with budding ramets emerging from the sand at high densities.
The designation of Solanum cowiei, along with the recent description of Solanum zoeae and allied unnamed variants in the Kimberley region (Barrett 2013), brings the count of cryptically dioecious Solanum taxa in Australia to 15. The preponderance of this unusual breeding system in this Australian lineage continues to generate questions regarding the evolution of the condition (e.g., Martine and Anderson 2007) and related ecological interactions (Dugan and Martine 2013, Martine and Evans 2013).
The poor resolution of the relationships among Australia’s dioecious Solanum species is a function of both overlapping morphological characteristics (see Symon 1980) and general difficulties in defining lower level relationships across all Old World “spiny solanums” (Bohs et al. 2007, Vorontsova et al. 2013). Further resolution of the relationships among Australian taxa will hopefully be achieved by combining greater sampling of populations (especially in the Kimberley) with Next Generation molecular techniques (C.T.Martine, studies in progress).
- Martine, C; Symon, D; Evans, E; 2013: A new cryptically dioecious species of bush tomato (Solanum) from the Northern Territory, Australia PhytoKeys, 30: 23-32. doi
- National Land and Water Resources Audit (2002) Native Vegetation in Australia: Major Vegetation Groups. Natural Heritage Trust, Commonwealth of Australia. www.environment.gov.au/atlas
- Anderson G, Symon D (1988) Insect foragers on Solanum flowers in Australia. Annals of the Missouri Botanical Garden 75: 842–852. http://www.jstor.org/stable/2399372, doi: 10.2307/2399372
- IUCN (2013) IUCN Red List of Threatened Species. Version 2013.2. www.iucnredlist.org
- Cowie I, Lewis D, Stuckey B (2011) Flora and Vegetation Survey of Limmen National Park (proposed), Northern Territory. Northern Territory Herbarium, Department of Natural Resources, Environment, The Arts and Sport, Northern Territory Government, Technical Report Number 20/2011D, Palmerston.
- Lewis D, Hill J, Cowie I (2010) Bullo River Station Flora and Vegetation Survey and Reconnaissance Soil-Landscape Investigation, Northern Territory. Northern Territory Herbarium, Department of Natural Resources, Environment, The Arts and Sport, Northern Territory Government, Technical Report Number 02/2010D, Palmerston. http://lrm.nt.gov.au/__data/assets/pdf_file/0016/17431/bullo_river_survey.pdf
- Symon D (1980) A revision of genus Solanum in Australia. Journal of the Adelaide Botanic Garden 4: 1-367.
- Martine C, Lavoie E, Tippery N, Vogt F, Les D (2011) DNA analysis identifies Solanum from Litchfield National Park as a lineage of S. dioicum. Northern Territory Naturalist 23: 29–38. https://www.academia.edu/1535437/DNA_analysis_identifies_Solanum_from_Litchfield_National_Park_as_a_lineage_of_S._dioicum
- Barrett R (2013) Solanum zoeae (Solanaceae), a new species of bush tomato from the North Kimberley, Western Australia. Nuytsia 23: 5–21. http://florabase.dpaw.wa.gov.au/science/nuytsia/655.pdf
- Martine C, Anderson G (2007) Dioecy, pollination and seed dispersal in Australian spiny Solanum. Acta Horticulturae 745: 269–285. http://www.academia.edu/1535452/Dioecy_pollination_and_seed_dispersal_in_Australian_spiny_Solanum
- Dugan G, Martine C (2013) Sex-differential insect herbivory in dioecious Australian nightshades. Abstract. Botany 2013, New Orleans, LA July 27–31. http://www.botanyconference.org/engine/search/index.php?func=detail&aid=586
- Martine C, Evans E (2013) Is inaperturate pollen produced by Australian dioecious Solanum a false reward for pollen foraging bees? Botany 2013, New Orleans, LA July 27–31. http://www.botanyconference.org/engine/search/index.php?func=detail&aid=487
- Bohs L, Martine C, Stern S, Myers N (2007) Phylogeny of the Old World clade of the spiny solanums (Solanum subg. Leptostemonum). Abstract. Botany and Plant Biology Joint Congress, Chicago, IL July 7–11. http://2007.botanyconference.org/engine/search/index.php?func=detail&aid=1868
- Vorontsova M, Stern S, Bohs L, Knapp S (2013) African spiny Solanum (subgenus Leptostemonum, Solanaceae): a thorny phylogenetic tangle. Botanical Journal of the Linnaean Society. doi: 10.1111/boj.12053