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

H. 0880_OR 426990_ WA H. 1645 _OR427010_ WA H H.. 0889 0888_ _OR OR 426998 426997 _ _AusVic AusVic R. baculifera H G.. 1643 428_ _ OR OR 427007 427008_ WA H HV. 1643 02287 _OR _OR 426992 426999 _ WA _AusVic H LT. 1644 0393 _ _ OR OR 427009 427011 _ _ WA WA R. psammophila HV 02531_OR426995 _ WA LT 0394_OR427013_ WA H. 1644 _OR426993_ WA HV02531 _OR427012 WA H. 1645 _OR426994_ WA R. psammophila LT 0351_OR427014_ WA G LT. 428 0393 _OR _OR 426991 426996 _ WA _ WA H H.. 0880 0889 _ _ OR OR 427005 427006 _ _ WA AusVic R. baculifera LamZech _AY 942164 R. tomentosa HV 00788_FJ 432658_ Philippines AD. A 88388_JQ082489_ Australia NOU 203447_ MT 782683_ Tuvalu R. sp. G. 736_JQ082489 _AusGBR R. orientalis NOU 203446_ MT 782675_ Tuvalu G. 737_JQ082488 _AusGBR NOU 087400 _ MT 782791_Solomon NOU 087399 _ MT 783175_SolomonIslands NOU 087399_ MT 782812_ Solomonlslands NOU 204070_ MT 783075_ Fiji R. diaphana H. 0864_JQ082495 _ WA ( R.nigrescens) NOU 087400_ MT 783157_SolomonIslands H. 0847_ JQ082496 _ WA ( R.nigrescens) R. diaphana NOU 204069_ MT 783198_ Fiji AD. A 88388_JQ082497_AusGBR ( R.orientalis) H H.. 0864 0847 _ _FJ JQ 432646 082490 _ _ WA WA R. nigrescens NOU 204070_ MT 782694_ Fiji NOU 204022_ MT 782720_ Fiji H. 0994 _OR427000_ Fiji NOU 204069_ MT 782837_ Fiji NOU 203063_ MT 783121_NewCaledonia NOU 204021_ MT 782778_ Fiji NOU 203014_ MT 783112_NewCaledonia NOU 087382_ MT 782691_ Fiji H NOU. 0995 203813 _OR427001 _ MT 783170 _ Fiji _NewCaledonia R. penicilloides NOU 203063_ MT 782746_NewCaledonia NOU 203014_ MT 782733_NewCaledonia NOU NOU 203950 203317 _ _ MT MT 783172 783115_ _ NewCaledonia NewCaledonia NOU 203813_ MT 782804_ NewCaledonia R. penicilloides NOU 203936_ MT 782839_NewCaledonia NOU 203936 _ MT 783200_NewCaledonia NOU 203317 _ MT 782737_ NewCaledonia NOU 203119_ MT 783082_NewCaledonia NOU 203950 _ MT 782807_NewCaledonia NOU 203161_ MT 783128 _NewCaledonia NOU 203119_ MT 782702_NewCaledonia NOU 203160_ MT 783156_NewCaledonia NOU 203276_ MT 782734_ NewCaledonia NOU NOU 203276 203098 _ _ MT MT 783113 783177 _ _ NewCaledonia NewCaledonia R. sp. NOU 203258_ MT 782753_NewCaledonia NOU 203258_ MT 783127_ NewCaledonia NOU 203259 _ MT 782813_ NewCaledonia R. sp. NOU 203160_ MT 782790_ NewCaledonia NOU NOU 203259 203380 _ _ MT MT 783176 783105 _ _ NewCaledonia PNG NOU 203161_ MT 782754_NewCaledonia HV04325_ NC. 037365 NOU 203098_ MT 782814_ NewCaledonia GH 0011084_JQ082481_ Guam R. coppejansii NOU 203380_ MT 782726_ PNG HV04754 _OR427015_ PNG NOU 203351_ MT 783109 _ PNG NOU 203733_ MT 783196_ Madagascar PITI 044_JQ082492_ Guam NOU 203447_ MT 783064_ Tuvalu GH 0011084_JQ082491_ Guam R. sp. NOU 203446_ MT 783056_ Tuvalu HV04325_ NC. 037365_ PNG R. coppejansii SEY 522_OR427004_ Seychelles HV04768_ OR427016_ PNG SEY 279_OR427002_ Seychelles R. sp. NOU 203351_ MT 782730_ PNG SEY 472_OR427003_ Seychelles NOU 203733_ MT 782835 Madagascar NOU 203176 _ MT 783227_NewCaledonia NOU 203130_ MT 782785_ NewCaledonia NOU 203130_ MT 783153_NewCaledonia R. sp. NOU 203176_ MT 782869_NewCaledonia R. sp. 0.003 NOU 203256 _ MT 783206_NewCaledonia NOU 203256_ MT 782846_NewCaledonia

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 south-western 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) .