DOI: 10.15468/uzn5qv
title: Australian representatives of Macrostelia transferred to Hibiscus (Malvaceae), with the description of a new species

description: This dataset contains the digitized treatments in Plazi based on the original journal article Craven, Lyndley A., Pfeil, Bernard E. (2004): Australian representatives of Macrostelia transferred to Hibiscus (Malvaceae), with the description of a new species. Adansonia (3) 26 (2): 235-240, DOI: 10.5281/zenodo.5181368KEY WORDS Malvaceae, Hibiscus, Macrostelia, Australia. ABSTRACTThe Australian species of Macrostelia fall within the circumscription of Hibiscus and the two taxa concerned are transferred to the latter genus. A new species is described. Three new names are proposed: H. tozerensis Craven & B.E. Pfeil (based on M. grandifolia Fryxell), H. macilwraithensis (Fryxell) Craven & B.E. Pfeil (based on M. grandifolia subsp. macilwraithensis Fryxell), and H. propulsator Craven & B.E. Pfeil (for the new species).MOTS CLÉS Malvaceae, Hibiscus, Macrostelia, Australie. RÉSUMÉTransfert des représentants australiens de Macrostelia dans le genre Hibiscus (Malvaceae) et description d’une espèce nouvelle.L’espèce australienne de Macrostelia relève de la circonscription d’ Hibiscus et les deux taxons concernés sont transférés dans ce dernier. Une nouvelle espèce est décrite. Trois noms nouveaux sont proposés: H. tozerensis Craven & B.E. Pfeil (basé sur M. grandifolia Fryxell), H. macilwraithensis (Fryxell) Craven & B.E. Pfeil (basé sur M. grandifolia subsp. macilwraithensis Fryxell) et H. propulsator Craven & B.E. Pfeil (pour l’espèce nouvelle).HOCHREUTINER erected the genus Macrostelia Hochr. to accommodate two new malvaceous species from Madagascar, M. calyculata Hochr. and M. involucrata Hochr. (HOCHREUTINER 1952). The new genus was primarily distinguished by HOCHREUTINER from other genera of Malvaceae in having the petals proximally connate into a long tube; in other genera the petals are connate only at the very base. Subsequently a third Malagasy species was added to the genus, M. laurina (Baill.) Hochr. & Humbert (HOCHREUTINER 1955). FRYXELL extended the geographic range of Macrostelia to Australia and described a new species, M. grandifolia Fryxell, in which two subspecies were recognised, M. grandifolia subsp. macilwraithensis Fryxell and the autonymic subspecies (FRYXELL 1974).The Australian macrostelias were included in an analysis of chloroplast sequence data from the ndhF coding region and the non-coding rpl16 intron from a comprehensive sample of species of Hibiscus L. and other genera of Hibisceae (PFEIL et al. 2002). Macrostelia consistently nested within Hibiscus and, in a combined analysis of ndhF and rpl16 data, grouped in a well supported clade that also included species of H. sections Bombicella DC., Hibiscus and Lilibiscus Hochr., including the type of Hibiscus, H. syriacus L. Unfinished studies utilising ndhF data suggest that the Malagasy species of Macrostelia also nest within the clade containing the Australian Macrostelia species but are not grouped with them (PFEIL and BAUM unpublished data). In assigning the new Australian species to Macrostelia, FRYXELL (1974) noted that the Australian species lacked the degree of adnation of petals to staminal column that was characteristic of the Malagasy species. Our observations are in accordance with those of FRYXELL and we have further observed that the degree of petal adnation manifest in the Australian Macrostelia species is comparable to that in all the Hibiscus species we have examined. Taking their morphology into account with the results of the molecular sequence research, it would seem that the two groups of Macrostelia species are not as closely related as previously believed.Of the other morphological features discussed by FRYXELL (1974) wherein Macrostelia differs from Hibiscus, the most distinctive is that of leaf venation. Macrostelia has pinnately veined, unlobed leaves whereas Hibiscus fide F RYXELL (1974) has palmately veined and u s u a l l y p a l m a t e l y l o b e d l e a v e s (a l t h o u g h Hibiscus papuodendron Kosterm., at least, has pinnately veined leaves [pers. obs.]). Both types of leaf venation may occur in other groups of Malvaceae, however. FRYXELL (1999) records the leaves of Pavonia subg. Goetheoides (Gürke) Ulbr. as being pinnately veined (the term penninerved is used by FRYXELL) but the species of the other subgenera of Pavonia apparently have palmate venation. Pinnate venation in fact occurs within three clades of a broadly defined Hibiscus, namely Azanzae s.l. (H. papuodendron nests herein), Trionum s.l. (Pavonia nests here), and Hibiscus - Bombicella s.l. (Macrostelia nests here) (PFEIL et al. 2002). The molecular support for the basic structure and membership of these three clades is strong in both cpDNA (PFEIL et al. 2002) and nDNA (PFEIL et al. 2004) and pinnate venation must be regarded as a character with poor predictive power as to classification. It is pertinent that, even in species of Hibiscus s.l. with palmate venation, the palmate condition applies only to the proximal veins (which often are much more developed than the other veins); the distal veins are pinnate. In this group of plants the difference between palmate and pinnate venation may be more reflective of the relative degree of development of the veins than of a divergence in basic structure per se.It is our conclusion that Macrostelia included within Hibiscus may be a better taxonomic placement than if it is kept separate. Given the shared character states of apically free styles, capitate stigmas, sterile staminal column apices, lack of gossypol, and capsular fruit, pinnate venation is a weak character upon which to maintain a genus. However, given that the molecular systematics of the Malagasy species of Macrostelia have not yet been studied to the same extent as the Australian species, Macrostelia is being maintained in the interim for its Malagasy representatives. The necessary nomenclatural transfers of the Australian taxa are effected below. A new Australian macrostelioid species, H. propulsator Craven & B.E. Pfeil, is described also. Although FRYXELL’ s two subspecies of M. grandifolia are generally similar in their leaves, the flowers are very different (Fig. 1). The epicalyx segments are free in subsp. macilwraithensis and 6-7 in number, whereas in subsp. grandifolia they are connate for about half their length and 4-5 in number. In addition, the petals of the former are spreading at anthesis and white, and of the latter are erect at anthesis and pale pink. These distinctive differences are maintained in wild and greenhouse-grown material and no intermediate forms have been seen, thus we believe that subsp. macilwraithensis warrants recognition at species rank. The collector of two collections of M. grandifolia, the late L.J. BRASS, indicated through specimen label annotation (on Brass 19352, 19353) that the species was dioecious. FRYXELL suggested that the species might best be described as gynodioecious as the “staminate” herbarium specimen he examined had fully developed styles and stigmas (FRYXELL 1974). The flowers of the Australian representatives differ in epicalyx and corolla form and are illustrated in Figure 1. Observations by us of living plants of each of the Australian species shows that the species have hermaphrodite flowers but are strongly protandrous. At early anthesis, the style branches are small, erect and appressed to each other, with the stigmatic hairs not readily evident; at this stage the anthers have dehisced and pollen is available for dispersal. Over the next few days, the style branches elongate, separate and spread widely such that the stigmas, which by now have well developed stigmatic hairs, may be brought into contact with the stamens. In nature, it is expected that insects probably would have removed the pollen from a flower prior to the stigmas becoming receptive; thus ensuring that the flower outcrosses. In the greenhouse, however, the pollen remains with the anthers as insects that potentially could pollinate flowers are excluded; selfing presumably occurs as we have noted that fruit is commonly produced on one accession of subsp. macilwraithensis. The Australian “ Macrostelia ” species differ from the other Australian species of Hibiscus in that they commonly have several flowers in each leaf axil.