28 Comp. Newsl. 47, 2009 The South African aquatic genus Cadiscus (Compositae-Senecioneae) sunk in Senecio Bertil Nordenstam', Pieter B. Pelser^ & Linda E. Watson^ 'Department ofPhanerogamic Botany Swedish Museum ofNatural History Box 50007, S-104 05 Stockholm, Sweden bertil.nordenstam(« nrm.se ^Oklahoma State University, Botany Department 104 Life Sciences East, Stillwater Oklahoma 74078-3013, USA [email protected] linda.watson1Odaokstate.edu Abstract The South African monotypic genus Cadiscus E.Mey. ex DC. (Asteraceae- Senecioneae)isanaquaticherbwithsomemorphological featuresthatareunusual in the tribe (white ray-florets and coarse, awn-like pappus bristles) and others that are reminiscent of species of subtribe Othonninae (ecalyculate capitula, relatively few, broad and connate involucral bracts, and sterile disc-floret styles). Unexpectedly, however, both plastid and nuclear phylogenies provided strong evidencethatthegenus isdeeplynestedinSenecios.str. ofsubtribeSenecioninae. Theunusual morphology isexplainedasadaptationstoanaquatichabitat, andthe genus is sunk inSenecio asSenecio cadiscus B.Nord. & Pelser, nom. nov. Introduction CadiscusE.Mey.exDC. isamonotypicgenusofthetribeSenecioneaeerectedfor CadiscusaquaticusE.Mey.exDC,arareandendangeredaquaticherbconfinedto afewseasonalpondsorvernalpoolsintheWesternCapeProvinceofSouthAfrica. DeCandolle(1838)placed itamongCompositae incertaesedis,and laterauthors (e.g., Bentham 1873a, 1873b, Harvey 1865, Hemsley 1887) treated the genus in the Helenieae on the basis ofits coarse and rigid pappus (Ornduff et al. 1967). In 1967, Ornduff etal. noticed moiphological similarities between Cadiscus and Othonna and allied genera and referred the genus to the Senecioneae, which was followed by later authors (e.g., Nordenstam 1968, 1977, 2007, Bremer 1994). , Comp. Newsl. 47,2009 29 More specifically, Ornduff et al. (1967) sought its affinities among members of subtribe Othonninae with which Cadisciis shares an ecalyculate involucre composed of relatively broad phyllaries that are connate in their basal half, a chromosome number ofn = 10, sterile disc floret styles, and white ray florets. Thesefeaturesare,however,notpresentinallOthonninaespecies. Inaddition,the stylesofCadiscusarequitedifferentfromthoseoiOthonna.TheCadisciisstyleis distinctly branched, has a truncate tuft ofsweeping-hairs, and even shows traces ofa divided stigmatic surface onthe inside ofthe branches, whereasthe Othonna style is simple, apically obtuse or conical with a collar ofvery short sweeping- hairs or papillae, and no stigmatic surface. In addition, taxa with white rays do occur in different genera within Senecioneae (e.g., Dollchoglottis, Urostemon, Daiiresia,Stenops,Senecios. str.)andnotonly inSouthAfrica.Theassignmentof Cadisciis to the Othonninae has therefore remained dubious orat least uncertain, and NoRDENSTAM (1968 p. 3If.) remarked that "the closer affinities ofthis little- known genus should be further investigated". Indeed, with its elongated stems rooting in the mud, erect flowering shoots with linear or lanceolate leaves, ecalyculatecapitulaborne singlyon simplepeduncles fromthe upperleaf-axils,a uniseriate involucre of8 to 10 partly connate phyllaries, coarse, basally flattened C pappus bristles ofray-florets, and sterile disc-floret styles, aqiiaticus is unique in Senecioneae and has therefore been hard to place. Our ongoing molecular systematic studies in the Senecioneae recently shed new light on the phylogenetic affinities ofCadisciis, placing it nested within Senecio s.str. (sensu Pelser et al. 2007). This phylogenetic position is well supported in both nuclearand plastid trees (Pelser et al. in prep.), and wetherefore advocate a transferofthe single species ofCadisciis to Senecio. SeneciocadisciisB.Nord.&Pelser,nom.nov.,proCadisciisaqiiaficiis E.Mey. ex DC, Prodr. 7(1): 255 (1838), nbn Senecio aquaticiis Hill nee S. aqiiaticus LoisEL. nee S. aqiiaticus Boiss. - Lectotype (designated here): South Africa, [Western Cape], Zwartland in Dumpfel R. I., Drege 1734, ^Widisciis aqiiaticus E.M." (G-DC sheet 1). Original material collectedby Drege ispresent in otherherbaria, viz. Drege s.n. ''Cadisciisaqiiaticus E.M. a"(G-DC,K.NY, S, SAM);''Cadisciisaqiiaticus EM. b" (S). De Candolle (1838) cites the locality as "ad Zwartland, in Dumpfel", whereasDrege(1843)hastwomoregeneralizedlocalities,viz.,"AmDassenberg, (zwischen Paardeberg und GroeneklooO, unter 500 Fuss. September" (litt. a on his herbarium labels; Drege 1843, p. 102), and "Zwischen Groenekloof und Saldanhabaai, unter 500 Fuss. September, October" (litt. b; Drlgi 1843, p. 113). The lectotype chosen here is the only specimen with locality statement agreeing exactly with the protologue. 30 Comp. Newsl. 47, 2009 Some ofthe morphological peculiarities ofthe species are no doubt explained by the unusual habitat. The development ofnarrow leaves, some ofwhich may be floating, and white flowers, is reminiscent ofotherwaterplants such as subgenus Batrachium of Rarninculus (Ranunculaceae). The coarse and awn-like pappus bristles may be an adaptation to zoochory, perhaps dispersal by waterfowl. This may also be an explanation for the presence ofmyxogenic hair tufts on the cypsela base. Mucilaginous cypsela hairs, due to being soaked in water, occur in differenttaxawithin the subtribe Senecioninae, particularlyamongthoseadapted to dry areas (e.g., Bolandia, Dauresia, Euryops spp., Jacobaea, Mesogramma, Psednothchia,), however the concentration ofsuch hairs to the basal part ofthe fruitisanunusualorevenuniquefeature.Thefloweringcapitulaof5". cadiscusare exposedtopollinators on erectpeduncles abovethewatersurface, but its fruiting heads seemtobebornemore orless atthewatersurface level (Fig. 1).Apossible dispersal scenario is that in the fruiting stage, when the phyllaries are broken up and shed, the fruits are exposed to dispersal agents. Inthis stage, the mucilage on the cypsela base might make the fruits adhere to the receptacle until the coarse pappusbristlessticktoadisperser,suchasawaterfowl,andthediasporeiscarried away. Observations on dispersal agents and mechanisms should be made in order to confirm these speculations and empirically ascertain the role ofthe unusual pappus and myxogenic cypsela hairs. Senecio cadiscus is locally endemic in the Western Cape Province, nowadays endangered and found only in some vernal pools or ponds between Malmesbury andHopefield(Goldblatt 1978,Bond&Goldblatt 1984,Goldblatt&Manning 2000). In2007, ErnstvanJaarsveld foundthespeciestobe still locallycommon in ponds at Philadelphia turnoff from Malmesbury road (Tierhoogte) and at Mamre Road near Darling. Acknowledgements We thank Ernst van Jaarsveld, SANBI, for information on Senecio cadiscus habitats in the Western Cape, and John Manning, SANBI, for useful referee commentsandthephotographinFig. 1. Dr. LaurentGautier(G)kindlyprovided information om the original material in Herb. G-DC. References Bentham, G. 1873a. Compositae. Pp. 163-533 In: Bentham, G. & J. D. Hooker (eds.), Generaplantarum 2. Lovell Reeve, London. 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Taxon 56: 1077-1104. 32 Comp. Newsl. 47, 2009 Fig. 1. Senecio cadiscus B. Nord. & Pelser in its natural habitat, Soutii Africa. Western Cape Province, Hopefield,August 1995. Photo J. Manning.