Hibiscus krichauffianus, F.Muell.

McLay, Todd G. B., Barker, Robyn M. & Albrecht, David E., 2023, Morphological and environmental variation within Hibiscus krichauffianus (Malvaceae), and the recognition of two new species, H. verecundus and H. calcareus, Australian Systematic Botany 36 (6), pp. 457-477 : 461-466

Morphological variation within H. krichauffianus sens. lat.

Specimens of Hibiscus krichauffianus were sorted into four morphotypes. A representative specimen of each is shown in Fig. 2 , seeds in Fig. 3 and typical habitats of morphotypes A–C in Fig. 4 . The morphotype encompassing the largest number of specimens, including those from NT and Vic., and many from SA, Qld and NSW was assigned morphotype A ( Fig. 2a , 3a , 4a ). The morphotype encompassing the second largest number of specimens, all from eastern Qld, was assigned morphotype B ( Fig. 2b , 3b , 4b ). Specimens from the Nullarbor region of WA and SA, along with those collected as far east as near Wilcannia in western NSW were assigned morphotype C ( Fig. 2c , 3c , 4c ). Specimens from the Murchison region in WA, of which only four were available for study (there were five specimens in total in herbaria), were assigned morphotype D ( Fig. 2d , 3d ). Features distinguishing the morphotypes are summarised in Table 1 and the distribution of each morphotype is shown in Fig. 1 .

Environmental variation within H. krichauffianus sens. lat.

PCA ( Fig. 5 ) shows a clear segregation of morphotype B samples (orange triangles) from morphotype A (grey squares), C (blue circles) and D (black crosses) samples. Morphotypes A, C and D largely occupy the same space within the PCA and the environmental variables used in the final dataset do not differentiate the climate envelopes of those morphotypes. Given the association of morphotype C with calcrete or limestone soils, edaphic variables may be more suitable for discriminating this species but were not included due to the lack of a comprehensive soil dataset for Australia (though see https://portal.tern.org.au/metadata/ 22160, accessed July 2023).

Taxonomic implications

We have shown that there is considerable morphological variation within H. krichauffianus and that four morphotypes can be distinguished.

After reviewing the putative type material (including the collection localities of specimens), we determined that morphotype A correlates with H. krichauffianus sens. strict. An amended description of H. krichauffianus , designation of a lectotype and identification of possible syntypes are presented below. The status of the name H. krichauffianus var. chippendalei Fryxell was investigated and is discussed below under excluded taxa.

Morphotype B can be distinguished from the other three morphotypes on the basis of several morphological characters and has a distinct environmental envelope relative to the other three morphotypes ( Fig. 5 ). This morphotype is described below as the new species H. verecundus McLay & Albr.

Morphotype C is similar to morphotype A ( H. krichauffianus sens. strict.), differing in the shorter stature and growth form, smaller and often more deeply toothed leaves and seeds with an indumentum of short appressed hairs ( Fig. 2–4 ). The consistent morphological differences between morphotype C and H. krichauffianus sens. strict., and the association of this morphotype with finer-textured calcareous soils (e.g. Milthorpe & Cunningham 1928, NSW 624403; Symon NYPE-1300, AD 98805401), indicates that this entity is worthy of formal recognition and is described below as H. calcareus McLay & Albr. The environmental variables we used did not capture the association of this taxon with calcareous soils ( Fig. 5 ).

Morphotype D is tentatively recognised as distinct on the basis of the ferruginous indumentum, petals longer than 39 mm long and geographic separation from other H. krichauffianus sens. lat. taxa. We have given morphotype D the informal phrase name H. sp. Belele (D.W.Goodall 3417). Further collections are required to confirm the morphological and environmental differences identified in this study that were based on limited material (five sheets in total).

Informal conservation assessments were made using International Union for Conservation of Nature (2012) criteria, though this should be more rigorously considered, and assessments also made against the threat classification system in use for each Australian state in which the taxa occur.

Taxonomy

Key to Hibiscus krichauffianus and related species

1. Epicalyx lobes fused at the base for more than 4 mm or if fused for less than 4 mm then free part never narrowly linear nor with a length to width (l:w) ratio higher than 4:1...... H. sturtii complex

Epicalyx free or fused at base for less than 4 mm, free part narrowly linear with a l:w ratio higher than 4:1........................................... .....................................................2 H. krichauffianus and allies

2. Young branchlet indumentum yellowish-brown; adaxial leaf surface green to dark green; stipules 0.1–0.17 mm wide; epicalyx lobes free or fused at base for up to 0.5 mm, free part straight in flower and fruit; seeds less than 2.5 mm long, with a patchy covering of appressed hairs.......................................................H. verecundus

Young branchlet indumentum white, silvery-white, grey or yellowish-white; adaxial leaf surface whitish, greyish, silvery or ferruginous; stipules 0.16–0.5 mm wide; epicalyx lobes free or fused at base for up to 3.5(–4) mm, free part straight in flower and becoming recurved in fruit; seeds 2–3 mm long but if less than 2.5 mm long then with a sparse to moderate covering of non-appressed hairs.............................................................................3

3. Branchlet indumentum becoming ferruginous on older branchlets; adaxial leaf surface silvery–ferruginous; epicalyx lobes free or fused at base for up to 1 mm; petals 39–42 mm long, apparently purple; seeds with a patchy covering of appressed hairs .............. ...............................................H. sp. Belele (D.W.Goodall 3417)

Branchlet indumentum not becoming ferruginous with age; adaxial leaf surfaces not ferruginous; epicalyx lobes free or fused at base for up to 3.5(−4) mm; petals 17–44 mm long, pale pink or mauve; seeds with covering of appressed or non-appressed hairs............4

4. Erect or ascending shrub or subshrub to ~ 1 m high, growing in deep sands; leaf lamina 10–55 mm long and 5–35 mm wide, flat to weakly concave or weakly folded in transverse section, the sinus between marginal dentations never reaching halfway to the midvein, pedicel abscission point usually 1–2 mm from the base; seeds rounded in profile with an indumentum of wispy hairs that are not regularly appressed (see Fig. 3a )......... H. krichauffianus

Low, spreading dome-shaped or rounded shrub to ~ 0.5 m high, growing on plains with lime-rich soils; leaf lamina 6–28 mm long and 4–16 mm wide, mostly strongly concave to folded or conduplicate in transverse section, the sinus between at least some marginal dentations reaching halfway to the midvein; pedicel abscission point usually in the upper half of the flowering stalk, 2–17(–24) mm from the base; seeds angular in profile with an indumentum of short, rigid appressed hairs (see Fig. 3c ).............. ................................................................................... H. calcareus

Figures

Fig. 2. Example herbarium specimens of the four morphotypes of H. krichauffianus sens. lat. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: C.J.Brodie & P.J.Lang 3402, AD 249644); (b) morphotype B Hibiscus verecundus (voucher: R.J.Fensham 2991, BRI AQ653057); (c) morphotype C Hibiscus calcareus (voucher: P.Hudson s.n., AD 98321044); and (d) morphotype D Hibiscus sp. Belele (voucher: D.W.Goodall 3417, PERTH 3427285). Scale bar: 2 cm.

Fig. 3. Seeds of the four morphotypes. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: C.J.Brodie & P.J.Lang 3402, AD 249644); (b) morphotype B Hibiscus verecundus (voucher: R.J.Fensham 2991, BRI AQ653057); (c) morphotype C Hibiscus calcareus (voucher: P.Hudson s.n., AD 98321044); and (d) morphotype D Hibiscus sp. Belele (voucher: D.W.Goodall 3417, PERTH 3427285). Scale bar: 1 mm.

Fig. 4. Habit of morphotypes A–C. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: D.E.Albrecht 16356, CANB; images: Dave Albrecht); (b) morphotype B Hibiscus verecundus (voucher: T.G.B.McLay TM333, CANB; images: Mike Bayly); and (c) morphotype C Hibiscus calcareus (voucher: D.E.Albrecht 16345, CANB [holotype]; images: Dave Albrecht).

Fig. 1. Distribution map for the four morphotypes of H. krichauffianus sens. lat. in Australia. Distributions are based only on material viewed by the authors. Morphotype A: Hibiscus krichauffianus sens. strict., grey squares; Morphotype B: Hibiscus verecundus, orange circles; Morphotype C: Hibiscus calcareus, blue triangles; Morphotype D: Hibiscus sp. Belele (voucher: D.W.Goodall 3417), black crosses.

Fig. 5. PCA of environmental envel- opes for four Hibiscus krichauffianus sens. lat. specimens sorted by morpho- type groupings. Morphotype A, grey squares; Morphotype B, orange circles; Morphotype C, blue triangles; and Morphotype D, black crosses.