Althenia hearnii T. Macfarlane & D.D. Sokoloff, 2017

Althenia hearnii T. Macfarlane & D.D. Sokoloff View in CoL , sp. nov. ( Fig. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 ).

Althenia hearnii has the following combination of character states unique among members of the genus: stigma circular in outline, centrally peltate, the margin entire; plants dioecious; female flowers on elongated pedicels, well exserted from the associated leaf sheaths; anthers 6-thecal.

Type: — AUSTRALIA. Western Australia: between Tammin and Cunderdin, road verge on Wyola North Road adjacent to Wyola Nature Reserve , 8 Sep. 2016, C.I. Fomichev 756 & T.D. Macfarlane (holotype PERTH 08775818 ; isotypes AD, CANB, K, MEL, MW 0595615, NSW, NY, PERTH 08775826 ) .

Lepilaena sp. Wheatbelt (M.T. Collins et al. 265) Western Australian Herbarium, in FloraBase, http://florabase.dpaw.wa.gov.au/ [accessed 10 March 2016]

Dioecious annuals, usually rhizomatous, with adventitious roots arising at nodes. Rhizome branching sympodially, lateral branches with scale-like prophylls. Plant height varying, short, from 1.5 cm and consisting of only one to three nodes, especially males, to elongated, slender, branched, up to 20 cm (both sexes but especially females). Small-sized male plants possessing only scale-like leaves below the inflorescence and adventitious roots at nodes of inflorescence. Larger male plants and all female plants possessing vegetative parts of the shoots below the inflorescence bearing long internodes and foliage leaves with sheath 3–6 mm long(membranous margins c. 0.75 mm wide), inconspicuously veined, distally auricled, not ligulate; blade 9–25 (–50) mm long, erect, not rigid, of uniform width until narrowing slightly just below the apex, flat, 0.1–0.25 mm wide, with a midvein (vascular bundle) and a band of 1–3 unlignified fibres at each margin, rather obscure, margins smooth, apex entire, acute, smooth. Elementary units of male inflorescences (terminating axes of different orders) compact, without long internodes, each unit containing several ligulate leaves with broad membranous sheaths surrounding successively maturing male flowers. Outer leaves in male inflorescence units with conspicuous long blades similar to those in foliage leaves below the inflorescence. Distal parts of some blades die off by the time of anthesis. Inner leaves in male inflorescence units with progressively shorter blades (up to minute scarcely visible appendages). Male flowers 1.5–1.6 mm long; perianth c. 0.3 mm long, of three free broadly triangular thick tepals, that are apiculate at anthesis; anther 0.9–1.1 mm long, 0.5–0.6 mm wide, 6-thecal (12-sporangiate), very rarely 4-thecal (8-sporangiate), dehiscing by six (very rarely four) longitudinal slits, with a minute flat brown terminal sterile apiculus; pedicels of male flowers at anthesis ca. 0.5 mm long, anther exsertion from enclosing leaf sheaths not observed. Female inflorescences lax, branching, without compact units. Leaves in female inflorescence eligulate, with narrow sheaths and distal auricles, resembling foliage leaves below the inflorescence, but blade usually shorter, 2–14 mm long and margins of auricles usually erose or irregularly toothed. Distal branches of female inflorescences with a pair of closely spaced leaves, a terminal flower and a stalked lateral branch repeating this pattern. Scale-like bracts in female inflorescences absent. Pedicel of female flower resembling the adjacent lateral branch, erect, slender, straight or flexuose, 1.5–11 mm long, exserted from the leaf sheaths, elongating to full length soon after anthesis; tepals 3, free, 1.8–2.7 mm long, membranous, veins obscure, apex erose or irregularly several toothed, sometimes shortly bifid as well (then divided to 1/5–1/3 of the length); carpels 3, as long as or just slightly exceeding the tepals at anthesis, with stalks 0.4–0.6 mm long, longer than the ovary, which is ellipsoidal, ca. 0.3 mm long; style slender, of uniform thickness, straight to flexuose, not rigid, much longer than the ovary, elongating considerably after anthesis and exposed beyond the tips of the tepals; stigma funnel-shaped, circular in outline, centrally peltate, the margin entire, appearing somewhat irregular when dried. Fruiting carpels with top of fruit conspicuously shorter than to almost equalling the tepal apices, the body of the fruit (“fruiting ovary”) brown, smooth but with a raised line along each side, 1–1.2 mm long, slightly flattened-terete, ovoid-oblong in outline, usually a little broader at base than apex, length/width ratio 2–2.4; style and stigma persisting at fruiting stage.

Other specimens seen (paratypes):— AUSTRALIA. Western Australia: Mt Narryer [Station], Murchison River , 1893, I. Tysson [Tyson] 14 ( MEL 3905 ) ; 6 miles (9.6 km) S of Coorow , 23 Aug. 1969, A.S. George 9516 ( PERTH) ; Mortlock Creek, Wongan Hills , 194 km NE of Perth, 21 Sep. 1974, K.F. Kenneally 2232 ( PERTH 01172824 ) ; Gazetted Reserve 7502, 1.5 km S of Robert Bay, Peel Inlet , 11 Oct. 1993, B.J. Keighery & N. Gibson 1065 ( PERTH 04544498 ) ; on E side of Kellerberrin-Shackleton Road, 2.5 km N of Bruce Rock-Quairading Road, Shackleton Nature Reserve, c. 32 km SSE of Kellerberrin [Plot - KL01], 31 Aug. 1999, G.J. Keighery & N. Gibson 4699 ( PERTH 06820581 ) ; Site 106A(Aq), salt lake E of Kondut South Road, 2.9 km SE of intersection of Kondut South Road with Northam - Pithara Road , 6 Oct. 2008, M.T. Collins, S.M. Jones & M.N. Lyons 265 ( PERTH 08077312 ) ; same location, 6 Oct. 2008, M.T. Collins, S.M. Jones & M.N. Lyons 266 ( PERTH 08077320 ) ; same location, 11 Sep. 2008, S.M. Jones, C.J. Francis & D.A. Halliday 2 ( PERTH 08077843 ) ; same location, 18 Nov. 2008, M.T. Collins & D.A. Halliday 221 ( PERTH 08077851 ) ; same location, 6 Oct. 2008, M.T. Collins, S.M. Jones & M.N. Lyons 220 ( PERTH 08077878 ) ; same location, 18 Nov. 2008, M.T. Collins & D.A. Halliday 222 ( PERTH 08077886 ) ; same location, 12 Sep. 2008, S.M. Jones, C.J. Francis & D.A. Halliday 3 ( PERTH 08077894 ) ; Site 115C(Aq), salt lake 4.1 km N of centre of Ballidu on the Northam - Pithara Road , second salt lake on the left, 9 Oct. 2008, M.T. Collins & S.M. Jones 227 ( PERTH 08077908 ) ; between Tammin and Cunderdin, small lake on western edge of Wyola Nature Reserve near Wyola N Road [type location], 23 Sep. 2014, M.D. Barrett & D.D. Sokoloff 102 (MW 0595614, PERTH 08775834 ) .

Taxonomic relationships:— This species has most often been previously identified as Lepilaena cylindrocarpa (Körnicke in Mueller 1861: 3) Bentham (1878: 180) [= Althenia cylindrocarpa (Körnicke in Mueller 1861: 3) Ascherson 1889: 213], but sometimes as Lepilaena preissii [= Althenia preissii ( Lehmann 1846: 3) Mueller (1888: 443) ]. These two species are regarded by us as the two most likely to be confused with this species. Althenia cylindrocarpa and A. preissii , like A. hearnii , possess 6-thecal (12-sporangiate) anthers, linear leaves 0.1–0.2(0.3) mm wide and smooth fruiting ovaries ( Jacobs & McColl 2011). The clearest difference between the new species and the other two species is the centrally peltate, circular funnel-shaped stigma as against the obliquely peltate funnel-shaped to spathulate stigma of the other two species. The centrally peltate stigma does not occur in any other currently named Australian species. The fruit colour is similar to that of A. preissii , whereas the fruits of A. cylindrocarpa are lighter brown to greenish when mature. The female flower is long-pedicellate and conspicuously exserted from the associated leaf sheath in the new species and in A. cylindrocarpa , but almost sessile and enclosed in the sheaths in A. preissii ( Jacobs & McColl 2011) . In addition, in the new species the female flower is usually solitary at each node except the terminal one, whereas in A. cylindrocarpa there are usually two or more female flowers at a node (and likewise in A. preissii )–these wordings are purely descriptive, and exact patterns of inflorescence architecture still need to be investigated. The new species and A. cylindrocarpa are consistently dioecious whereas A. preissii is often monoecious, with mixed groups of male and female flowers, although some populations are dioecious.

Distribution and habitat:— Known from seven locations including four in the Wheatbelt, one from near Peel Inlet, south of Perth, and one from well north of the other records, from the Murchison River on Mt Narryer Station. Three of the Wheatbelt locations are from close to each other in the Wongan Hills area, and the other two are from further south near Shackleton and Tammin. The plants have been recorded as growing in dense aquatic herb-fields, in shallow brackish to salty water in lakes or wetlands, in clay or sandy clay soils, usually associated with one or more of samphires ( Tecticornia species, Chenopodiaceae ), species of Ruppia ( Ruppiaceae ) or stoneworts (all three are represented in the population shown in Figure 3 View FIGURE 3 ). Mixed collections of this species have been found with three other species of Althenia .

Phenology:— The plants germinate when the habitat becomes wet after autumn rain, commence flowering in late August or early September, continuing into October as older female flowers develop and mature as fruit, and dying off in November as the water dries through evaporation.

Conservation status:— Not considered at risk at present.

Etymology:— The specific epithet hearnii acknowledges the contribution of Roger William Hearn (born 1954), former Regional Ecologist with the Department of Parks and Wildlife, Manjimup, to understanding salinity in Western Australia, especially in the Muir-Unicup catchment, and to improving knowledge of and facilitating research on aquatic plants, including this genus.