Corynanthera, a New Genus of Myrtaceae

Corynanthera,a new genusof Myrtaceae (Subfamily Leptospermoideae,Tribe Chamelaucieae)

By J. W. Green (WesternAustralian Herbarium)

Abstract

_ Corynanthera.fluvo J. W. Creen gen. et sp. nov. is describedan

CorynantheraJ. W. Greengen, nov,

Frrl//.r racemis te[minalibus_spiciformibus. Folia opposita decussata. F/o/er solitarii, axxrarec.TJgomorpht,.tubo dorst\.enrraliLer comprerso. StaminalO: filarnenloin qlipite nlll9fTr qfod !1919 .Clandem rerm,inalem ferente. Anrheraeunilocu lares foro uno dehiscenres, mlcro\poranglrsJ In uno ptanodlsposjLis. Ovarium uniloculare. Orrll2. ad venamsrylarem po5lrcamrn parte o\arii renia collateralileramj.i_

Type species: C.-Jlaya,I,. W. Green, the only known species. The generic name refers to the clublike appendagesassoCiated with ihe anthers.

Shrub wjth small, estipulate, decussate leayes. Jnflorescencea terninal or sutr-terminal spikeJike raceme.. Flowers solitary, in-the axils of the upper-tibe teaves, sub,tended by two persistent bracteoles, zygomorphic; florcl o,orsrventrafty_compressed._the tree.part inclined towards the axisl sepals 5, the ?ntedor 2 larger and the posterior smaller than the other 2; pitqli 5, ex- ceedingthe sepals. Slazcrs 5 F 5. in two scarcelydistinguishable whorls, the outer, antepetalous stamens with the filament irroducei into a filiform stipe bearing a large, irregularll-shapedor 1 globuiar appendageabore rhe anlner:.1neInner. tntesepalous. stamens uith a shorterfilament and a smaller, elllpsordal. appendage level with the outer anlhers, Anthers versatile, sub- globular (some$hat dorsi\entally.compressed). uniplanar. trisporangiate, ynilocular, with ore micro-sporangiumabove and two below. introrre] de_ hrscfng,bya pore. central . Ova.ryinferror. the uall consistingofa thin, fibrous, granourar,ouler layer. a broad aere_nchymalousmiddle zone and a fragile, membrano-usin_ner layeri locule l, small, in the upper half or third. placZnti lateral wthtn the ovary. attached to the stylar vein which passesjust inside the outer layer.onthe posreriorside. Ovrles2. ellipsoidal.collaterally atrached aDo\e.lne,.mrddle. ,Aerenchymaand m_embranebreaking do$n. presumably arrer.Tenl Zatron. (herr place apparen y eventually becoming occupied by rne srngreseec. Jee.1not seenmature. Within Chamelaucieae..which .., ,the aredistinguished by a unilocularovary wrlh a srngleplacenta and indehiscen_t.dry fruit \ ith l_2 seeds(Bentham 1867), Corynanthera falls into a small group -of genera contalniig Tht1,p_ tomene,and Micromynus, most species of which have 5 or 10 free itamefs, regularfyopposrte sepaisor pelals.without 5tamiDodia. Corynonthera,while sharing lhese characteri5ticswith Thryptomeneand Micromyrtus, is distin_ suished.fromboth generaby its trisporangiate.unilocular ant-hers,the associ_ ated. drmorphrc appendages and the spikeJike inflorescence of closely- appressed,yellow flowers. I

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Figures 18 26. Corynantheraffava. 18, T.S. Inflorescence,showing centtal axis, ante- petalous anthers (p) (upper), antesepalousanthe$ (s) (lower), floral tube at two levels of ovules(ov) (left and right); 19, Flower, L.S. showing antepetalousstamen (lelt), antesepalous stamen(right) and developingseed; 20, Antepetalousanther and gland, L.S. showingstomium (st) alter dehiscence;2l-25, Anther-2l, tangential L.S. showing three mjcrosporangia 22, T.S. upper sporangium-23, T.S. above stomium showing three sporangia-24, T.S. below stomium showingtwo sporangia 25, T.S. showingfibrous-banded endothecium (et), junction of t\,r'o sporangia and pollen grains; 26, Floral tube and bracteoles,T.S. showing ovary, including ovules (ov), inner wall layer (i) and middle layer (m) (all frcm Green 4917).

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prorlerqptor.rerur:nueurulor 90"#fi"t':;BlTi,i"l eror,lr€d.Duera *"t"0",;t:3,'ir"J,liT,r-:'eclldllla-0]Bl c.o errdrrs'eduot u.iru i + erouetx: oujtuots etea'E3uol ulLll S'l '/'l'J :eiet 'e3uci1 i:nLi f rou i.6-97.g'Ellenbreul egeln ltltuos D/rdrg Lunlelso] rert^elalDto[- wnin t tRgot!JJ|J-Ja-c.7'satlsses.sr.rolr'seluelssr>cl)opal)Dtgeduol uJ L-Z DlluDsatoq :errlorlleotsnd[e tsntle 'snltoJo 'slllJer8 -4'*eauo1 uitu 9-!.1 zrloJ ur.: 511-gg x'r'{ '17-1 sa:nE1g-',Lou'ds uae:g 'd|I c^8UaJaqluBu,{roJ yellow. Anthers reddish-purple, 0.3 mm diameter. Filamentous continu- ation of the filament 0.3 mm long, curved over the anther, yellow. ,tf//e 0.5 mm long, the stigma at maturity level with the inner anthers. Selectedspecimens (all PERTH): 35 miles (56 km) W of Winchester, C. Chap- man, 14 Nov. 19751'25km W of Winchester,J. Il. Green 4917,6 Dec. 1978' 30 kn WSW of Winchester, J. ll. Green 4920, 6 Dec. 1978; 43 km SW of Winchester,J. W. Green4919,6 Dec. 1978; 39 miles (62 km) W of Coorow, C. Chapman,15Jan.1967l. Within 24 miles(38 km) W of Coorow, C. Chapman, 4 Jan. 1976; N end of Watheroo National Park, J. S. Beard 7880, 18 Sept. 1976;E boundary of Watheroo National Park, R. D. Rolce 9721,7 OcL 19'Il. Conserration ,s/alrJ: Density ranges from sparse to locally abundant. Pop- ulations occur in three National Parks. Because of the very small area of occuffence, however, and because the species has already proved attractive to the cut flower trade, it should be protected from commercial exploitation in the wild. Efforts are being rnade to bring it into cultivation. Distribution: an elliptical area some 70 km long, extending from Tathra Nat- ional Park to Watheroo National Park, about 200 km north of Perth, Western Australia (Figure 27). Habitat: heaths and shrublands where it is frequently associated with Xylo- meluru angustifoliun, Eucalyptus todtiana and Eucalyptus eudesmoideson pale, grey-brown, somewhat loamy sands over laterite. Annotated voucher speci- mens of the associated speciesare deposited in the Western Australian Herb- arium (PERTH). Flowering period: Septernberto February.

Discussion

The anther of Cor),nantheramay be described, using the terminology of Green (1980), as trisporangiate and unilocular (Figures 20-25). This is in sharp contrast with the remainder of the Myrtaceae which are only known to have tetrasporangiate anthers (Davis 1966), apparently always bilocular. The sporangia are uniplanar, as described by Prakash (1969) rn Darwinia mtcf opetqn, Two of the above characteristics of Corynanthera appear to be unique in the angiosperms. No record has been found in the literature of a iri- sporangiateanther. Eames (1961,p.114) noted that antherswith more than four sporangia were uncommon ot rare, except in forked or branched stamens, and that the larger number was nearly always eight, even this sometirnes "nearly resulting from connation. He regarded a smaller number, always two", as representing.a reduction from the basic four, giving several examples of bisporangiate families and genera. The only example glven of any oiher reduced number was Arceuthobium (Viscaceae)which has "with a single sporangium some trace of a second". lt seemsreasonable to speculatethaa the apparently trisporangiate anther of Corynanthera may be tetrasporangiate in origin.the appendageharing arisenfrom a fourth. sterilesporangium. Arother apparently unique feature of Cory)nantherais the single, porate, posterior stomium (Figures 8 9, 11-12,20), through which Dassthe coments of the three micro.porangia(figure 2lJ at anrhisis. Thus Lhe remainins \estigesof threemicrosporangial complrtments are hereinlerpreted as coml prising a singleloculus_(Green 1980J. Further embryologicalstudy may reveal the pore to be morphologicallyterminal, which would be-unusualin thi aneio- sDermsbut not unioue. 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Evidencethat the spongy aerenchymamay sometimespersist in older flowers or fruits is contained in the original description of Mitomyrtus sul- phurea, in which Fitzgerald (1904) noted "fruiting calyx somewhatspongy within."

Acknowledgments I am indebted to my colleaguesfor helpful discussionand to Mr. C. Chapmanof Winchester,W.A. for collectingspecimens and assistingme to locate occurrencesin the field. Mr. P. G. Wilson read the manuscriDtand Mr. A. S. Georgeprovided the Latin diagnoses. Mrs. J. W. Lee-Frampton is thankedfor technicalassistance.

References BENTEAM,G. (1867). "Flom Austmliensis" v. 3 (Reeve: London.) BLACK,J. M, (1952). "Flora of South Austmlia.", 2nd ed. Pt. 3 (Covt. Printer: Adelaide.) DAvIs, G. L. (1966). "Systematic Embryology of the Angiosperms." (Wiley: New York.) EA[cs, A. J. (1961). "Morphology of the Angiosperms." (Mccraw-Hill: New York.) ESAU,K. (1965). l'Plant Anatomy." (Wiley: New York.) FAqN, A. (1952). On the structure of floml nectaries. Bot. Gaz, 113: 46+70. "Plant FAHN,A. 0974). Anatomy", (Pergamon: Oxford.) FITZGERALD,W. V. 0904), Additions to the West Australian flora. J. W. Austral. Nat. Hist. Soc. 2(1): 3-36. GREEN,J. W. (1961). The Eenrs Conostylis R.Br. II. Taxonomy. Proc. Linn, Soc. N.S. Wales85: 33+373. GREEN,J. W. 0980). A revised terminology for the spore-containingparts of anthers New Phytol. 84 (iri press). KERNERvoN MARTLAUN,A. & OLrvER,F. W. (1902). "The Natural History of Plants," 2 Yols.(Blackie: London.) PRAKASH,N. (1969). Reproductive development in two species of Dorwi ia Rudge (Mlrt- aceae). Austral. J. Bot, l7 i 215-27.