Solanum watneyi Martine & Frawley, 2016

Martine, Christopher T., Frawley, Emma S., Cantley, Jason T. & Jordon-Thaden, Ingrid E., 2016, Solanum watneyi, a new bush tomato species from the Northern Territory, Australia named for Mark Watney of the book and film " The Martian ", PhytoKeys 61, pp. 1-13 : 2-8

Solanum watneyi Martine & Frawley sp. nov. Figs 2 , 3

Diagnosis.

Solanum watneyi is distinguished from Solanum eburneum by its weakly erect and sprawling habit, long internodes and fruiting pedicels, often scabrous dark green leaves, dusty purple corollas, and lemon-yellow thickly-walled ellipsoidal fruits often held on or near the ground.

Type.

AUSTRALIA. Northern Territory: Judbarra/Gregory National Park, Bullita Stock Route, 6 km north of Bullita Campground turnoff, 16°03.100"S, 130°27.201"E, 6 May 2014 (staminate and hermaphrodite flowers; fruit), Christopher T. Martine and Rachel F. Martine 4065 (holotype: DNA; isotypes: BUPL, CONN)

Description.

Weakly erect to sprawling sub-shrub to 50-60 cm. Rhizomatous and apparently clonal. Stems slender, woody, often bending to ground, especially when weighted by fruits; initially single stemmed, with strong lateral branching beginning at ca. 5-10 cm; internode lengths on mature stems averaging about 4 cm. Overall plant aspect dark green to gray-green, with older stems eventually pea-green to yellow-brown; pubescent throughout with porrect stellate trichomes (stems, leaves, pedicels, calyces) with stalks 0-0.1 mm long, lateral rays 6-10, central ray (midpoint) 1-1.5 times as long as the lateral rays; pubescence of stems short and loose. Prickles sparse, straw-colored, straight, slightly widened at base, fine, 2-5 mm long, scattered on stems. Sympodial units difoliate, the leaves solitary or geminate. Mature leaves 12-16 cm × 2-6 cm, alternate, lanceolate-elliptic, with 6-8 pairs of primary veins; young leaves lighter green and gray-hairy but becoming dark green above, slightly paler beneath, both sides closely and densely stellate tomentose, older leaves becoming scabrous and uniformly dark on both sides, retaining dense tomentum along veins; base attenuate; margins entire, sinuate or occasionally shallowly 6-8 lobed; apex rounded, mucronate; scarcely armed along midvein beneath; petiole 3-3.5 cm long with few to no prickles. Inflorescence a supra-axillary andromonoecious cyme 9-11 cm long, consisting of a basal hermaphrodite flower and a distal group of 3-7 (usually) staminate flowers (the most basal staminate flowers occasionally expressing as hermaphrodite), typically 1-2 staminate flowers open at a time, common peduncle typically 2-5 mm (-20) long, rachis slightly less tomentose than stems. Flowers 5-merous, heterostylous. Hermaphrodite flower ca. 2.5 cm below the staminate flowers, opening first; pedicel 2-3 cm long at anthesis, elongating further after fertilization, armed with prickles 2-5 mm long; calyx lobes 5-8 mm long, armed with long, straight prickles and stellate trichomes; corolla 4-5 cm in diameter, dusty purple, rotate; acumens ca. 2 mm; ovary glabrous, ca. 2 mm diameter at anthesis; style 11-12 mm (including capitate stigma), curved; stamens equal; filaments ca. 1 mm; anthers 6 mm long, oblong-lanceolate to somewhat tapered, poricidal at the tips, in a loose anther cone. Staminate flowers with pedicels 15-16 mm long, unarmed or with few prickles; calyx lobes 7-8 mm long with a few 3-4 mm weak prickles or prickles absent, the lobes ending with a slender filiform acumen ca. 3 mm long, slightly reflexed; corolla 2.5-4.5 cm in diameter, dusty purple, broadly stellate to rotate; acumens ca. 0.5 mm; stamens of same proportions as in hermaphrodite flower; ovary, style, and stigma vestigial and not exserted beyond the stamens. Fruit an ellipsoidal berry 2-2.5 cm long, 1.5-2.2 cm wide, light green with dark green stripes when young, maturing to lemon-yellow with faint brown stripes; flesh firm, the locules 2, not liquid-filled and the internal cavity dry, the fruit wall ca. 0.5 cm thick, the fruits retained on plant after maturation. Fruiting pedicels 3.5-4.5 cm long, deflexed so fruits resting on ground at maturity. Fruiting calyx enclosing and exceeding fruit in early development, eventually covering up to 2/3 of developed fruit, the lobes long-acuminate, blunt-tipped, and weakly reflexing as fruit matures, short stellate-pubescent and armed with sharp spines 2-5 mm long, these single or paired along the calyx sutures, the lobes often fused in a 3+2 or 4+1 arrangement. Mature seeds up to ~100 per fruit, 2.5-3.5 mm, tan to dark brown, finely reticulate.

Distribution and ecology.

Solanum watneyi is presently known from a small range of localities in the sub-arid, monsoon-influenced, zone of northwestern Northern Territory (Fig. 1 ) at elevations around 100-150 m. The species is locally abundant along the Bullita Stock Route and nearby areas, but abundance elsewhere is not well known. Solanum watneyi appears to be associated, at least in Judbarra, with the "Ridges, Hogbacks, Cuestas, and Structural Plateaux" land unit defined by Brocklehurst et al. (1996), where it occurs in open Eucalyptus woodlands. Field collections have been made in well-drained limestone-based soils variously described as being sandy, sandy-loamy, clayey-loamy, and loamy. Collections from 70-80 km east of the Bullita section suggest that the species range extends eastward into the Wanimyn Trust and the landscapes around the Buchanan Highway; and collections from Limbunyah Station hint toward a westward range extending toward the Western Australia border (Fig. 1 ).

The areas where Solanum watneyi has been collected most frequently are along graded roads (Fig. 2D ), suggesting that this taxon is disturbance-adapted. Although collections have been made in areas that experience bushfires, specific fire ecology adaptations are unknown. The pollination biology has not been studied, but the flowers are likely buzz pollinated (see Anderson and Symon 1988) - as evidenced by anthers with terminal pores and the need for physical manipulation of anthers during hand pollinations in cultivation. Seed dispersal appears to be biotic given the fleshy nature of the fruits, which ripen to yellow at maturity. Symon (1979) included Solanum eburneum in a group of solanums with firm yellow berries likely to be dispersed by mammals or larger birds; Solanum watneyi fits this same profile.

Phenology.

Most flowering specimens have been collected from March-May, at the transition from the wet to dry seasons, with fruiting specimens collected in April-June. Earlier flowering collections (e.g. K. Brennan 9002, 27 Jan 2000) suggest that blooming may begin during the rainy season and extend into the dry season. Plants in cultivation began flowering about 90 days after seed germination; and fruits took about 60 days to mature following hand pollination.

Etymology.

The specific epithet of “watneyi” is inspired by the book and film, The Martian, in which the protagonist finds himself stranded on Mars surrounded by the planet’s harsh terrain and reddish soils. In a shelter, he manages to grow a crop of potatoes ( Solanum tuberosum ) before finally being rescued by his astronaut colleagues. We’ve chosen to name Solanum watneyi after this character, Mark Watney, in part because of the similarly reddish soils of its habitat and the congeneric nature of the potato - but, most notably, as a way to honor the creation of a sci-fi hero botanist by author Andy Weir ( Weir 2013) and to acknowledge perhaps the finest paean to botanical science (and botanical field work) that Hollywood has yet presented (see Martine 2015).

Preliminary conservation status.

Based on IUCN Red List Categories ( IUCN 2012), Solanum watneyi should be considered Data Deficient (DD). While the species appears to be relatively widespread over a range of approximately 6000 km2, it has been collected in fewer than 20 localities. The small number of collections, coupled with the fact that populations often consist of multiple individuals, suggests that the species is common in some localities but uncommon on the regional and global scales (apparently of restricted distribution). Further data are required before a certain conservation status can be determined. Key populations are protected in Judbarra/Gregory National Park and appear secure.

Specimens examined.

AUSTRALIA. Northern Territory: Bullita Homestead (ca. 8 km north), 16°03'--"S, 130°26'--"E, 14 Apr 1996 (fr), P.K. Latz 14752 (NT); Gregory National Park, Bullock Paddock Creek area, 16°11'21"S, 130°28'59"E, 13 Apr 1996 (fr, fl), G.J. O’Neill 3 (DNA); Humbert River Station, 16°42'S, 130°40'E, 14 Jun 1974 (fr), P.K. Latz 5325; Bullock Paddock Creek, 16°6'55"S, 130°17'27"E, 13 Apr 1996 (fl), M. Woodward 94 and R. Booth; Gregory National Park, N. of Bullita Homestead, 16°06'57"S, 130°25'26"E, 11 Apr 1996 (fl), N.G. Walsh 4185 (DNA); Gregory National Park, 16.07°S, 130.24°E, 6 Feb 1986 (fl), B.G. Thomson 1185 (DNA/NT); Jasper Gorge area, 16°1'59"S, 130°42'3"E, 27 Jan 2011(fl), K. Brennan 9002 (DNA); Judbarra/Gregory National Park, Bullita Stock Route, 32 km south of Victoria Highway, 16°00.491'S, 130°27.952'E, 5 May 2014 (fl, fr), C.T. Martine and R.F. Martine 4061 (BUPL); Judbarra/Gregory National Park, Bullita campground, 16°06.802'S, 130°25.394'E, 5 May 2014 (juv), C.T. Martine and R.F. Martine 4063 (BUPL); Judbarra/Gregory National Park, Bullita Stock Route, 6 km north of Bullita Campground turnoff, 16°03.100'S, 130°27.201'E, 6 May 2014 (fl, fr), C.T. Martine and R.F. Martine 4065; Judbarra/Gregory National Park, 8 km north of Bullita campground, 16°01.103'S, 130°27.790'E, 5 May 2014 (fl, fr), C.T. Martine and R.F. Martine 4067 (BUPL).

Discussion.

Solanum watneyi has been known for some time as a recognized morphotype, having been described by Latz as Solanum sp. “Bullita” in the early 1970s. This name has been used as an identifier by other botanists since that time (e.g. Bean 2012), appearing on the labels of herbarium specimens that are similar to Solanum eburneum yet conspicuous enough in the characters identified above to merit attention.

Previous studies inferred that Solanum eburneum is part of the "Bush tomato clade" ( Martine et al. 2006, 2009), a clade of andromonoecious species that appears to have arisen between 4 and 1.5 million years ago ( Särkinen et al. 2013). Preliminary results from a large-scale next generation molecular study (Martine et al. in prep) infer that Solanum watneyi is most closely related to Solanum eburneum and Solanum chippendalei . Solanum watneyi stands out among this group based on morphological differences that include its conspicuously long fruiting pedicels and internodes, lighter purple corollas, and a sprawling habit that often finds mature fruits resting on ground.

In the western (Bullita) tract of Judbarra/Gregory National Park, Solanum watneyi is locally common along the roadsides of the Bullita Stock Route between the Victoria Highway and the old Bullita Homestead, where it has been collected numerous times. Its abundance along this dirt thoroughfare suggests that the species appears, like many solanums, to respond favorably to disturbance. In fact, it appears most vigorously on the edges of graded dirt roads, resprouting from rootstocks after passes from mechanized grading equipment (Martine, pers. obs.)

While our ex situ morphometric analyses and most field observations are consistent with the distinctive morphological gestalt of Solanum watneyi , collections from around the Bullita Station can be somewhat confusing - with vegetative characters approaching intermediacy between it and Solanum eburneum . A small set of ex situ crosses between them (Martine, unpublished) suggests that interspecific hybridization is possible. Symon (1981) described Solanum eburneum as a narrowly-occurring species of "broad, shallow, seasonally dry Melaleuca swamps or flats with heavy grey soils" around the East Baines River. This localized endemism aligns with the characteristic physiography described by Brocklehurst et al. (1996) for the East Baines corridor, with Solanum eburneum occurring on clays and lithosols found on alluvial plains and rises along the river course as it runs northwest out of the Bullita section of the park (and on Dick Creek to the west and Timber Creek to the east). The presence of Solanum watneyi on well-drained sandy-loamy soils on the (largely) southern edge of this range suggest that the two closely related taxa might have diverged on disparate soil types in the last few million years (dating based on Särkinen et al. 2013).

Recent land use history may have brought the species into secondary contact on the north-south edge of their ranges in the central area of the Bullita Section, where an underlying geology including sandstone, siltstone, and dolomite creates an especially complex physiography ( Brocklehurst 1996). The remote Bullita cattle station, the homestead of which is now a park attraction and outstation site, operated in this area for several decades beginning in the early 1900s. The Bullita Stock Route, a graded access road running south from the Victoria Highway, closely parallels the East Baines River near the homestead - providing a corridor of frequently disturbed habitat by which Solanum eburneum and Solanum watneyi might move and come into contact with the aid of road grading equipment or, perhaps historically, livestock. We suggest that the combined effect of ancient-origin physiography and recent disturbance in this area has created a zone of hybridization that deserves further study.

Figures

Figure 1. Distribution map of Solanum watneyi and Solanum eburneum based on accessions held by DNA, BUPL and CONN. Specimens of Solanum eburneum mapped are cited in Appendix 1.

Figure 2. Illustration of Solanum watneyi. Mature branch with flowers and a developing fruit. Based on plant grown at Bucknell University from seeds of Martine and Martine 4065. Drawing by Rachel F. Martine.

Figure 3. Comparisons of Solanum eburneum and Solanum watneyi. A-C Solanum eburneum in habitat (gray cracked clay), in flower, and mature fruits D-F same for Solanum watneyi (habit showing reddish sandy loam) G corolla comparisons of staminate (upper) and hermaphrodite (lower) flowers for Solanum eburneum (left) and Solanum watneyi (right) H leaf shape across varying leaf ages for Solanum watneyi (top) and Solanum eburneum (bottom) in cultivation; I) field growth habit of Solanum eburneum (left) and Solanum watneyi (right) showing the more sprawling and prostrate nature of Solanum watneyi. Photos A, C, D, E, F, I by CTM; B, G by JC; H by EF.