Rhipilia psammophila Huisman & Verbruggen, 2023

Huisman, John M. & Verbruggen, Heroen, 2023, A morphological and molecular study supports the recognition of Rhipilia psammophila sp. nov. and Rhipilia baculifera comb. nov. (Halimedaceae, Chlorophyta) from southern Australia, Australian Systematic Botany 36 (6), pp. 427-436 : 428-433

Rhipilia psammophila Huisman & Verbruggen , sp. nov.

Type: Two Peoples Bay , Western Australia, in sand at 2 m depth, 2 Jan. 2022, J. M.Huisman 2.1.22.1 (holo: PERTH 09389660 [four specimens are mounted on the sheet; the holotype is the specimen shown in Fig. 3 c ]; iso: PERTH 09389679 [with four specimens on the sheet]) .

Thalli dark green, psammophytic, erect, soft and spongy, up to 10 cm tall (including holdfast) and 7 cm broad, arising from a fibrous matted base, with a subterete short stipe grading into an upper flabellate to cuneate blade. Structure of interwoven terete siphonous filaments, lower filaments 40–70 μm in diameter, upper filaments 60–100 μm in diameter (broadest in fertile filaments), these branched at irregular intervals, with or without shallow constrictions at dichotomies. Lower filaments with short to long lateral branches arising perpendicularly, with constrictions just above the base, forming attachments to adjacent filaments via terminal tenacula, these with 2–4 mostly blunt prongs that occasionally divide once more. Filaments heteroplastic, with numerous round to ellipsoidal chloroplasts 3–5 μm long. Reproduction by profuse basally constricted gametangia arising laterally on upper filaments. Gametangia clavate to obovoid, often onceforked, 145–580 μm long and 45–140 μm broad ( Fig. 3 ).

Habitat

Growing in sand among seagrasses ( Posidonia K.D.Koenig and Amphibolis C.Agardh ). At Two Peoples Bay in southwestern Western Australia, the species was seen to be locally common, but restricted to sandy habitats between the extensive seagrass beds that dominate the bay ( Fig. 1 ).

Etymology

From the Greek psammos ‘sand’ and philos ‘loving’, in reference to the species’ habitat.

Notes

Rhipilia psammophila , with its flabellate thallus, structurally with branched siphons attached to one another by tenacula, is typical of what was until recently regarded as Rhipilia ( Millar and Kraft 2001; Verbruggen and Schils 2012). However, on the basis of molecular analyses, Lagourgue and Payri (2021) segregated several species of Rhipilia and Rhipiliopsis as their new genus Kraftalia , in doing so accommodating species with and without tenacula in a single genus. However, there was no suggestion that individual species can vary in this respect, so the presence of tenacula remains a useful character for species delimitation.

Our molecular analyses place Rhipilia psammophila in a clade with the type species of Rhipilia ( R. tomentosa Kütz. ) and other species of the genus as defined by Lagourgue and Payri (2021). Those authors included in Rhipilia species with widely diverging morphologies, but with some consistent features, including the presence of a stolon (although R. tomentosa has been observed without a stolon), siphon dichotomies with a subdichotomous bulge and supra-dichotomous constrictions, and simple tenacula (2 or 3 prongs). Siphon diameters are 20–320 µm. Kraftalia was characterised by Lagourgue and Payri (2021) as having a fan-shaped frond, no stolon, relatively thin siphon diameters (<100 µm in diameter) that are dichotomously divided with or without supra-dichotomous constrictions, and the cohesion of siphons by one or more particular types of structures (direct longitudinal contact, papillae, differentiated siphons, or tenacula). Four previously described Rhipilia and Rhipiliopsis species were transferred to Kraftalia and the authors recognised a further five as-yet undescribed species (none from Australia).

Thus, there is considerable morphological overlap between the two genera, seemingly separable only by the presence of a stolon and potentially larger siphon diameters in Rhipilia . On the basis of morphology, in particular the absence of a stolon and smaller siphon diameters, Rhipilia psammophila appears to align with Kraftalia ; however, our molecular analyses clearly align the species with Rhipilia . Although there were no obvious stolons, it is worth noting that the new species often grew in clusters, and there might have been horizontal buried siphons connecting the individual thalli.

Womersley (1984), in his monograph of the green algae of southern Australia, included several species of then Udoteaceae that display some habit similarities with Rhipilia psammophila , including Avrainvillea clavatiramea A.Gepp & E.Gepp , Rhipiliopsis peltata (J.Agardh) A.Gepp & E.Gepp , Rhipiliopsis robusta Womersley , and Rhipilia pusilla (Womersley) Ducker. Of these, only Rhipilia pusilla forms tenacula, but it is a much smaller plant (up to 1.5 cm tall), not compressed, and only the basal siphons are ‘weakly or not attached by lateral tenacula’ ( Womersley 1984, p. 247). Lagourgue and Payri (2021) included Rhipilia pusilla in their molecular analyses, but the results were somewhat equivocal, the authors preferring to leave the status of R. pusilla as ‘in question’. Of the known southern Australian taxa, the most similar in appearance are Rhipiliopsis peltata and Rhipiliopsis robusta ; however, siphons in these species are attached by circular or papillar fusions ( Womersley 1984, pp. 248–251; Kraft 1986, p. 49).

Of the tropical Australian species of Rhipilia documented by Millar and Kraft (2001), Kraft (2007) and Huisman and Verbruggen (2015), only R. tomentosa is described as sanddwelling. It differs from R. psammophila in the diagnostic regularly curved or bent siphons that attach to adjacent siphons, plus the deep constrictions that are plugged by internal rings of wall thickenings ( Millar and Kraft 2001, p. 26). Rhipilia tomentosa has been recorded from eastern Australia ( Millar and Kraft 2001), but according to Lagourgue and Payri (2021), the species is restricted to the Caribbean and records from other areas require confirmation with DNA sequences. They noted that Pacific specimens that were morphologically similar to R. tomentosa actually belonged to their new genus Kraftalia on the basis of DNA analyses. However, no species identity was suggested for these Pacific specimens.

Lagourgue and Payri (2021) regarded species in this group to be restricted to specific geographic areas, and on the basis of sequence analyses, morphological differences and the collection locality being far removed geographically and climatically from the distribution of all known species of Rhipilia , we herein recognise the Two Peoples Bay taxon as new.

Specimens examined

WESTERN AUSTRALIA. Two Peoples Bay , in sand at 2 m depth, 2 Jan. 2022, J.M.Huisman s.n. ( PERTH 09389679 ); loc. id., southern end of bay, 12 Nov. 2008, A.Dekker, C.Nutt, K.Murray & H.Botha s.n. ( PERTH 08188459 ); Hopetoun , on sand-covered rock, 12 Dec. 2012, H. Verbruggen HV2531 ( BR5010111415391 V); loc. id., attached in the sand, 12 Dec. 2012, L.Tyberghein LT0351 ( BR5010111416428 V) .

Figures

Fig. 3. Rhipilia psammophila. (a) Specimen in situ at Two Peoples Bay, Western Australia, growing among seagrasses. (b) Clustered specimens growing in sandy substrata. (c) The pressed holotype specimen (PERTH 09389660). (d) Siphons bearing perpendicular lateral branches with terminal tenacula (indicated by arrows). (e) Tenacula adhering to adjacent filament (indicated by arrow). (f) Fertile filaments with numerous lateral gametangia. (g) Closer view of lateral gametangia. Scale bars: 1 cm (c); 60 µm (d, e); 600 µm (f); 300 µm (g). Vouchers: (a, b, d, e) J.M.Huisman 2.1.22.1 (PERTH [holotype]); (f, g) A.Dekker, C.Nutt, K.Murray & H.Botha s.n. (PERTH 08188459). Photos: J. M. Huisman.

Fig. 1. (Caption on next page)