Hydrocotyle simulans A.J.Perkins, 2020

Perkins, Andrew J., 2020, Hydrocotyle simulans (Araliaceae), a new perennial species from south-eastern Australia, Phytotaxa 437 (2), pp. 66-72 : 67-71

Hydrocotyle simulans A.J.Perkins , sp. nov. ( Figs. 1 & 2A–2D )

Diagnosis: Hydrocotyle simulans is morphologically similar to the perennial species H. pterocarpa , but differs by having glabrous (vs. sparsely hairy to subglabrous) peduncles, flowers appearing sessile within umbels (vs. distinctly pedicellate), flowers with crimson petals (vs. cream petals often with reddish mottling), transversely lenticular (vs. distinctly flattened) mericarps and wingless (vs. prominently winged) mericarps with minutely rugulose (vs. smooth) surfaces when mature.

Type:― AUSTRALIA. Victoria: Bridgewater Lakes, Portland. 38° 19′S, 141° 24′E, November 1946, A. C. Beauglehole 669 (holotype: MEL 0723352!, isotype: MEL 0723353!).

Description:― Perennial herbs consisting of prostrate to ascending stems bearing leaves and umbellate inflorescences, 2–25 cm high. Roots fibrous, borne at nodes along prostrate stems. Stems pale green to reddish green, terete, glabrous. Stipules white to pale cream, occasionally pale reddish at the base, broadly ovate to orbicular, 1.0–2.0 mm long, 1.5– 3.0 mm wide, membranous, translucent, margins entire. Petioles 1–17 cm long, glabrescent with retrorse trichomes restricted to the upper quarter of petioles and with a ‘skirt’ of retrorse trichomes at their apices; trichomes white, simple, 1.5–2.0 mm long. Leaf blades simple, dorsiventral, carnose, orbicular-cordate to reniform in mature leaves, 5– 22 mm long, 7–30 mm wide; adaxial surface green, glabrous or subglabrous with 1–10 white erect trichomes; abaxial surface slightly paler in colour than adaxial, glabrous. Hydathodes present at the termination of veins along lamina margins. Leaf margins with 3–7 shallow lobes; lobing entire or with 1–3 teeth; teeth rounded to obtuse. Inflorescences leaf-opposed, simple umbels, anthesis centripetal, 5–14-flowered, 2–4 mm wide. Peduncles terete, much shorter than subtending leaf at anthesis and when in fruit, 3–28 mm long, glabrous. Floral bracts present, ovate to broadly ovate, mostly trilobed or rarely entire, pale green, glabrous, 0.8–1.4 mm long. Pedicels light green, terete, glabrous, distinctly shorter than subtending bracts, 0.1–0.2 mm long. Flowers all hermaphrodite, protandrous. Sepals absent. Petals 5, pale to dark crimson, ovate, 0.6–0.8 mm long, 0.4–0.5 mm wide. Filaments pale cream, 0.4–0.5 mm long. Anthers creamy yellow, elliptic, 0.2 mm long. Ovaries green at anthesis, bilaterally flattened, elliptic, glabrous. Fruiting pedicels terete, 0.2–0.6 mm long. Schizocarps bilaterally flattened, symmetrical, orbicular with cordate bases, pale green to reddish green turning brown to pale reddish brown at maturity; commissure 95% the length of mericarps. Mericarps glabrous with shallowly rugulose surface, distinctly biconvex in transverse section 0.9–1.4 mm long, 0.6–1.0 mm wide; dorsal rib conspicuous, acute; lateral ribs obscure to shallowly raised; median ribs obscure. Carpophores absent. Fruiting styles slender, terete, 0.4–0.6 mm long, reflexed.

Phenology:—Flowers and fruits mainly from October to June of the following year.

Etymology:—The specific epithet ‘simulans’ is derived from the Latin word ‘simulo’, meaning copy or imitate, and it refers to the resemblance of Hydrocotyle simulans to both H. pterocarpa and H. plebeya , based on general vegetative morphology.

Distribution: —Occurs in south-eastern South Australia, southern Victoria and Flinders Island, off the north-eastern coast of Tasmania ( Fig. 3 ).

Habitat:— Hydrocotyle simulans is typically found in freshwater swamps or on the margins of wetlands, often in coastal or nearby areas.

Additional specimens examined:— AUSTRALIA. Victoria: Moleside Creek, Lower Glenelg , 38°04’S, 141°19’E, 22 January 1950, A. C. Beauglehole 6559 ( MEL) ; Gippsland Lakes Reserve , 38°01’S, 147°32’E, 27 October 1984, A. C. Beauglehole 78969 ( MEL) ; Wilsons Promontory, Silver Swamp , 38°54’39”S, 146°17’33”E, 15 February 1989, E. A. Chesterfield 2232 ( MEL) ; Wilsons Promontory , 38°51’56”S, 146°11’58”E, 11 March 1989, E. A. Chesterfield 2309 ( MEL) ; Wilsons Promontory , 38°47’15”S, 146°27’45”E, 17 March 1989, E. A. Chesterfield 2420 ( MEL) ; Bridgewater Lakes, Cotters Lake, Wilsons Promontory , 38°56’S, 146°16’E, 18 March 1968, G. S. Hope s.n. ( MEL) ; Portland district , 38°19’S, 141°24’E, 4 April 1963, F. G. Swindley 1579 ( MEL) . Tasmania: Flinders Island , north-western corner of north-western arm of [an] e-shaped lagoon, 40°2’S, 148°13’E, 4 January 1984, J. S. Whinray 8130 ( MEL) ; Flinders Island, Hogan’s Lagoon , 39°51’S, 148°3’E, 6 June 1984, J. S. Whinray 8206 ( MEL) ; Flinders Island, Hogan’s Lagoon , 39°51’S, 148°3’E, 6 June 1984, J. S. Whinray 8207 ( MEL) ; Near Vinegar Hill, Lady Barron, Flinders Island , 0.5 mile NE of hill, 40°12’S, 148°15’E, 12 April 1954, J. H. Willis s.n. ( MEL) .

Discussion: — Hydrocotyle simulans has been overlooked and misidentified based on similarities of vegetative morphology and habitat with those of H. pterocarpa and H. plebeya . The link in morphological affinity between H. pterocarpa and H. plebeya was first established in 1855 by Mueller in his published protologue for H. pterocarpa ( Mueller 1855) . Mueller based this relationship on general morphological similarities of his gatherings of H. pterocarpa and herbarium specimens he had viewed of H. plebeya . The affinity between the two species was later reaffirmed by Bentham in his ‘Flora Australiensis’ treatment of Hydrocotyle ( Bentham 1867) . Bentham specifies that both species can be differentiated from each other based on the distinctly winged and laterally flattened fruit of H. pterocarpa ( Fig. 2E ), compared to the acutely ribbed and wingless fruit of H. plebeya ( Fig. 2F ; Bentham 1867).

The earliest gatherings of H. simulans in South Australia and Victoria were made in 1913 (R. Bates 3533) and 1946 (A.C. Beauglehole 669) respectively. The South Australian specimens were formally identified and determined to be H. plebeya by Black (1952) and Eichler (1986), because they possessed wingless schizocarps and acute ribs. However, closer examination of the herbarium specimens, including the type materials of H. plebeya , have shown them to possess a suite of discrete morphological differences when compared with H. simulans . This misapplication of H. plebeya to the South Australian specimens (held at AD) of H. simulans has been consistent when compared to the Victorian and Tasmanian (Flinders Island) specimens of H. simulans (held at MEL), where most specimens have been left undetermined or misidentified. As a result of re-circumscribing the South Australian herbarium specimens of H. plebeya to H. simulans , H. plebeya s. str. is now considered endemic only to the south-west of Western Australia.

The number of herbarium collections for H. simulans within Victoria and in Tasmania are restricted to four widespread geographic locations ( Fig. 3 ) and it is uncertain whether this truly reflects the rarity of this species (within these states) or that it has long been overlooked due to its (co-distribution and) vegetative similarity to H. pterocarpa . Comparisons of morphology and life history traits indicates H. simulans maybe more closely allied to H. pterocarpa than H. plebeya , based on both species being perennial in life history (annual in H. plebeya ), reflexed trichomes on the petioles (glabrous petioles in H. plebeya ) and ovate floral bracts with basal lobes (lanceolate bracts with irregularly toothed margins in H. plebeya ) ( Table 1).

Figures

FIGURE 1. Illustration of Hydrocotyle simulans (A–D). A: Flowering and fruiting plant showing habit; B: Flowering umbel; C: Lateral view of a dry, mature schizocarp showing acute lateral and dorsal ribs, and the minutely rugulose surfaces; D: Floral bract with basal lobes. Illustration by Andrew Perkins based on MEL 0723352 and MEL 0723353.

FIGURE 2. Photographs of Hydrocotyle simulans (A–D) and fruit of allied species H. pterocarpa (E) and H. plebeya (F). A: Hydrocotyle simulans—Flowering umbel showing flowers with crimson petals and an immature leaf showing a ‘skirt’ of reflexed trichomes at the petiole apex; B: Mature leaves; C: Lateral view of a dry, mature schizocarp showing acute lateral and dorsal ribs, and the minutely rugulose surfaces; D: Immature infructescence showing lenticular schizocarps; E: H. pterocarpa—Lateral view of a dry, mature schizocarp showing prominently winged mericarps; F: H. plebeya—An infructescence showing mature schizocarps with acute dorsal and lateral ribs and papillate mericarps surfaces. Scale bars A=2 mm; B=10 mm; C=500 µm; D=1 mm; E=1 mm; F=500 µm. Vouchers: D.E. Murfet 8999 (A, B, D); R.J. Bates 71336 (C); AD 96936300, I.B. Wilson 986 (E); PERTH 2298589, A.R. Annels 642. Photographs by Denzel Murfet (A, B, D); South Australian Seed Conservation Centre (C, E); Andrew Perkins (E).

FIGURE 3. Distribution of Hydrocotyle simulans in south-eastern Australia (z) based on specimens held at MEL, AD and CANB.