Solanum jobsonii Martine, J.Cantley, & L.M.Lacey, 2017

Lacey, L. Mae, Cantley, Jason T. & Martine, Christopher T., 2017, Solanum jobsonii, a novel andromonoecious bush tomato species from a new Australian national park, PhytoKeys 82, pp. 1-13 : 3-7

Solanum jobsonii Martine, J.Cantley, & L.M.Lacey sp. nov. Fig. 2

Diagnosis.

With affinity to Solanum eburneum , Solanum watneyi , and Solanum diversiflorum , but differing by the involute corolla margins, deeply dissected leaves with 6-12 lobes and smaller creamy-yellow fruits.

Type.

AUSTRALIA. The Northern Territory: Limmen National Park, on main road, 15°54'47"S, 135°31'43"E, elev. ca. 250 ft, 12 May 2010 (fl, fr), B. Stuckey & I.D. Cowie 645 (holotype [two sheets]: DNA)

Description.

Lax to weakly erect sub-shrub or short-lived perennial herb to 20-50 cm tall. Stems slender, woody, upright even when weighted by fruits; initially single stemmed, with strong lateral branching beginning at ca. 7 cm; internode length on mature stems ca. 1.5 cm. Overall plant aspect dark green to gray-green, becoming slightly more yellow-green with age; pubescence of stems short and loose; moderately to densely pubescent throughout with stellate stalked trichomes, the stalk 0.05-0.1 (rarely to 0.2) mm long, with 6-8 rays 0.2-0.4 mm long, the midpoint elongate, to 0.4 mm long. Prickles sparse to moderately dense, straw-colored, straight, slightly widened at base, fine, 1-6 mm long, scattered on stems. Sympodial units difoliate, the leaves solitary or geminate. Mature leaves 5-9 cm × 1.5-5 cm, linear to lanceolate or elliptic, with 1-4 pairs of primary veins, with only a few prickles along midvein on leaf undersides; young leaves lighter green and gray-hairy but becoming dark green above, slightly paler beneath, both sides closely and densely stellate-pubescent, the older leaves becoming scabrous and uniformly dark on both sides, retaining dense pubescence primarily only along veins; base tapering; margins deeply incised and 6-12 lobed, occasionally shallowly lobed or nearly linear; apex blunt; petiole 0.3-2.3 cm long with few to no prickles. Inflorescence a supra-axillary andromonoecious cyme 1-6.5 cm long, consisting of a basal hermaphrodite flower and a distal group of 2-5 (usually) staminate flowers; typically 2-5 staminate flowers open at a time; common peduncle typically 1.5-2.5 mm long; rachis slightly less pubescent than stems. Flowers 5-merous, heterostylous with a single hermaphroditic flower at the base of the inflorescence and the plants andromonoecious. Hermaphrodite flower ca. 1.5-3 cm below the staminate flowers, usually opening first or soon after lowest 1-2 staminate flowers; pedicel ca. 2 cm long at anthesis, elongating further after fertilization, armed with prickles 1-4 mm long; calyx lobes ca. 11-15 mm long and fused for first 2-3 mm, some pairs occasionally fused entirely with sepals arranged 2+2+1, armed with long, straight prickles and stellate trichomes; corolla 2.5-4.5 cm in diameter, medium purple, rotate, free of indumentum; stamens equal; filaments ca. 1.5 mm long; anthers 5 mm long, oblong-lanceolate to somewhat tapered, poricidal at the tips, in a tight anther cone; ovary glabrous, ca. 2 mm diameter at anthesis; style 6-11.5 mm long (including capitate stigma), curved. Staminate flowers with pedicels 9-14 mm long, unarmed or with few prickles; calyx lobes 6-10 mm long and fused for first 1-2 mm, occasionally 2+2+1 as above, with a few 1-4 mm weak prickles or prickles absent; corolla 2.5-3.5 cm in diameter, medium purple, broadly stellate to rotate; acumens ca. 0.5 mm long; stamens of same proportions as in hermaphrodite flower; ovary, style, and stigma vestigial and not exserted beyond the stamens. Fruit a globose berry 1.6-1.8 cm long, 1.5-2.0 cm wide, light green with darker green stripes when young, maturing to creamy yellow; flesh firm; locules 2, liquid-filled; fruit wall ca. 2.2 mm thick; fruits retained on plant after maturation. Fruiting pedicels 1.2-2.3 cm long. Fruiting calyx enclosing and exceeding fruit in early development, eventually covering 1/4 to 1/3 of developed fruit, the lobes narrowly triangular, long-acuminate, blunt-tipped, turning brown 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. Seeds up to ~135 per fruit, 2.8-3.6 mm long, dark brown to black, flat, reniform, finely reticulate.

Distribution and ecology.

Solanum jobsonii is presently known mostly from a restricted range of localities in Limmen NP in the sub-arid, monsoon-influenced zone of northeastern Northern Territory (Fig. 3 ) at elevations around 250 feet. The species is locally abundant in a few sites along and just off of the Nathan River Road, yet abundance elsewhere is not known. Solanum jobsonii is primarily associated with Eucalyptus pruinosa Low Open Woodland ( Cowie et al. 2011) on seasonally-flooded alluvial plain fringes (above seasonal streams) and plains. The most abundant population encountered in 2016 was in a Eucalyptus pruinosa Schauer subsp. pruinosa ( Myrtaceae ) woodland on grey-brown clay with limestone stones and laterite pebbles where the primary associated taxa were Melaleuca nervosa (Lindl.) Cheel ( Myrtaceae ), Dodonaea physocarpa F.Muell. ( Sapindaceae ), Dolichodandrone heterophylla (R.Br.) F. Muell. ( Bignoniaceae ), Grewia retusifolia Kurz ( Malvaceae ), Carissa lanceolata R.Br. ( Apocynaceae ), Eulalia aurea (Bory) Kunth ( Poaceae ), Calandrinia gracilis Benth. ( Portulacaceae ), herbs and grasses. Although S. jobsonii is nearly always found in E. pruinosa woodlands, the converse is not true; S. jobsonii was not present in many of the E. pruinosa stands in which we searched. This suggests that S. jobsonii is sensitive to fine-scale habitat variation that we did not observe.

Nothing is known about pollination biology or seed dispersal of S. jobsonii , but floral morphology aligns with the typical Solanum buzz pollination syndrome (see Anderson and Symon 1988) and the fleshy berries suggest biotic dispersal (see Symon 1979). Plants encountered in May 2016 bore numerous mature fruits that had not been taken by frugivores - a phenomenon also seemingly typical among close relatives.

Although S. jobsonii has been collected on the edges of graded roads and appears to be disturbance-adapted, the species only appears where these thoroughfares bisect otherwise suitable habitat where seasonal flooding is also apparent. Occasional bushfires figure prominently into the ecology of these sites, but the effect on S. jobsonii is unknown.

Phenology.

The few collections made of flowering material are from the early months of the dry season, April-June, but first flowers likely bloom during the wet season (November-March) given the observation of mature fruits in April and onward. Under greenhouse conditions S. jobsonii fruits mature around 60 days after hand pollination. Successful ex situ autogamous and geitonogamous pollinations infer that the species is self-compatible.

Etymology.

The specific epithet of " jobsonii " is selected to honor Peter Jobson, Senior Botanist at the Northern Territory Herbarium at Alice Springs, an expert on the Northern Territory flora and the leader of the 2016 expedition to collect this and numerous other Solanum taxa with the authors.

Preliminary conservation status.

Cowie et al. (2011) noted that Limmen NP is home to nearly 1200 plant taxa, including two, Seorsus intratropicus (F.Muell.) Rye & Trudgen ( Myrtaceae ) and Triodia longiloba Lazarides ( Poaceae ), for which Limmen is considered the primary center of their distribution. Solanum jobsonii follows the pattern of these two taxa in its being restricted to specialized habitats and being largely known from this single national park, thus we suggest that it also be added to the park’s list of species of conservation significance ( Cowie et al. 2011). The species is known from only four populations (even after much searching by the authors in other potentially-appropriate habitats), each consisting of a few dozen individuals. When evaluated using the IUCN Red List Categories and Criteria for extinction risk ( IUCN 2001), S. jobsonii falls into the Vulnerable (VU) category under Criterion B (B1ab(iii)+2ab(iii)). The VU designation is the lowest of three threatened categories, but indicates the taxon still faces a high risk of extinction in the wild. It has an Area of Occupancy <2000 km2 and Extent of Occurrence <20,000 km2, less than 10 known locations that are possibly fragmented, and observed decline in overall habitat quality. Suitable habitat will continue to decline without active conservation management.

Specimens examined.

AUSTRALIA. Northern Territory: Limmen National Park, just north of Lorella Springs turn off, 15°54'44"S, 135°31'42"E, 17 April 2008 (fl, fr), D.J. Dixon 1745 (DNA); Limmen National Park, Nathan River Road, 3.7 km north of Lorella Springs turnoff, 1 5.94913°S, 135.53464°E, elev. 246 ft., 14 May 2016 (fl, fr), C.T. Martine, J.T. Cantley, L.M. Lacey and P. Jobson 4226 (DNA, BUPL); Limmen National Park, jct. Lorella Springs Rd. and Nathan River Rd., 15.91605°S, 135.52926°E, 14 May 2016 (fl, fr), C.T. Martine, J.T. Cantley, L.M. Lacey and P. Jobson 4227 (DNA, BUPL); Benmara Station, approx. 1 km west No. 38 Bore, 17°54'--"S, 136°57'--"E, 5 June 1984 (fl), Strong 253 (DNA); Limmen National Park, along main road, 16°01'39"S, 135°33'24"E, 8 May 2010 (fl, fr), B. Stuckey & I.D. Cowie 595 (DNA); Savanna Way between Nathan River and Borroloola, 15°47'44"S, 135°25'46"E, 15 July 2008 (fl), H. van der Werff & B. Gray 222501 (DNA); Limmen National Park P, Nathan River Rd., Lorella Springs turnoff, 15°54'56"S, 135°31'46"E, 12 May 2010 (fl, fr), B. Wirff 531 (DNA).

Discussion.

Morphological comparisons of S. jobsonii and its close relatives, S. watneyi , S. eburneum , and S. diversiflorum , demonstrate a statistically significant difference among the four taxa. Most notably, S. jobsonii differs from the other three species by its involute corolla margins, deeply dissected leaves with 6-12 lobes, smaller creamy-yellow fruits, and a set of nine morphometric characters highlighted in Table 1 [including corolla diameter (in both staminate and hermaphrodite flowers), calyx lobe length, and length of the fruiting pedicel]. While leaf lobing can be a rather variable character within and between Solanum species, the deeply-cut sinuses of S. jobsonii (and the occasionally linear leaf lobes/blades) are quite visually distinctive - and this character holds up in comparison to the close relatives in both field collections and in cultivation. The new species maintains a distinct geographic distribution from its closely related congeners, inhabiting limited areas on gray-brown clayey soil with limestone stones and laterite pebbles in the region of Limmen National Park in the northeastern portion of the Northern Territory. The species is named after Peter Jobson, Senior Botanist at the Northern Territory Herbarium at Alice Springs, who organized and led the expedition during which the new species was most recently collected and confirmed as distinct. Solanum jobsonii is one of the first new plant species described from Limmen NP, an area that received formal protection in only 2012.

National parks are under threat throughout the world, with federally-protected lands in places like the United States in potential danger of being left unfunded, deforested, or sold into private ownership ( The Guardian 2017). By contrast, the 10,000 km2 Limmen NP is a new acquisition for the Northern Territory Government and, in its short time under protection, has already proved to be a cradle of impressive biodiversity ( Cowie et al. 2011). Notably, the use of trained biodiversity scientists in surveys of the proposed parkland provided masses of data in support of protecting this area as a national treasure. The discovery of the new species described here, and the potential description of other new forms of biodiversity from Limmen NP, is a testament to the benefits of not only investing in national parks in Australia and elsewhere, but also investing in parks-based scientific inquiry.

Figures

Figure 2. Solanum jobsonii Martine, J. Cantley, and L. M. Lacey and related species. A Typical habitat in clay soils with limestone stones and laterite pebbles, Limmen National Park, NT B S. jobsonii in flower and C in mature fruit D Corolla comparisons of staminate (upper) and hermaphrodite (lower) flowers for S. jobsonii (left) and S. diversiflorum (right) E Leaf shape across varying leaf ages for S. jobsonii (top) and S. diversiflorum (bottom) F S. jobsonii immature fruit with armed calyx G Corolla comparisons of staminate (upper) and hermaphrodite (lower) flowers for S. eburneum (left) and S. watneyi (right) H Leaf shape across varying leaf ages for S. watneyi (top) and S. eburneum (bottom) I Seed size, shape, and color comparisons from left to right - S. jobsonii, S. diversiflorum, S. eburneum, and S. watneyi J S. jobsonii trichome density of apical adaxial leaf surface (top) and apical abaxial leaf surface (bottom). Photos A, B, C, F, G by J. T. Cantley; H by E. S. Frawley; D, E, I, J by L. M. Lacey. Yellow scale bars: B, D, F, G = 1.5 cm; C = 5 cm; E, H = 2.25 cm; I = 8 mm; J = 1.5 mm.

Figure 3. Geographic distribution of S. watneyi, S. eburneum, S. diversiflorum, and S. jobsonii in eastern Western Australia and the Northern Territory, Australia, based on specimens held at the Northern Territory Herbarium Palmerston (DNA).