Centrolepis milleri M.D. Barrett & D.D. Sokoloff, 2015

Barrett, Matthew D. & Sokoloff, Dmitry D., 2015, Centrolepis milleri (Centrolepidaceae: Poales), a new species from Western Australia, Phytotaxa 213 (2), pp. 140-146 : 141-145

Centrolepis milleri M.D. Barrett & D.D. Sokoloff , sp. nov. ( Figs. 1–3 )

Type: — AUSTRALIA. Western Australia, Mt Benia Reserve, 30 ° 13’19.2” S, 115 ° 16’29” E, 12 October 2010, M.D. Barrett & B. P. Miller MDB 3186 (holotype: PERTH 0000 0000, isotypes: CANB, MEL, K).

Centrolepis sp. Eneabba ( B. P. Miller s.n. 31/12/2009), Western Australian Herbarium, in FloraBase, http://florabase.dpaw.wa.gov.au [accessed 9 January 2015].

Tufted annual 13–35 mm high ( Figs. 1 , 2A ). Primary root always present, 1.1–11 mm long. Adventitious roots up to 15 mm long usually present on epicotyl and/or nodes of leaf rosette, sometimes on the cotyledonary node. Roots on hypocotyl not recorded. Primary and adventitious roots 0.2–0.3 mm (in distal parts up to 0.4 mm) in diameter, with dense root hairs up to 0.5 mm long, usually branching up to the second order. Due to root curving just after departure of a lateral root, branching superficially resembles a dichotomy. Hypocotyl up to 5 mm long, ca. 0.2 mm in diameter, glabrous except in its basal slightly swollen part (collar) bearing absorbing hairs up to 0.5 mm long. Cotyledon ( Fig. 2A ) glabrous, 4–5 mm long; sheath open, 1–1.2 mm long with membranous margins; ligule and auricles absent; lamina assimilating but turning dark by anthesis, single veined, rounded in cross-section, 0.1–0.2 mm in diameter; tip haustorial, hidden in persistent seed coat, 0.3–0.4 mm long. There is no branching in the axil of the cotyledon. Epicotyl shortened or up to 4 mm long, 0.3–0.5 mm in diameter, glabrous. All shoots, including the primary shoot, possess a basal rosette composed of foliage leaves followed by cataphylls and ultimately form a terminal inflorescence. The primary shoot possesses at least three foliage leaves and up to five cataphylls. Lateral shoots may develop in axils of every foliage leaf and can further branch in the same way. Branching never takes place in axils of cataphylls. Lateral shoots (when present) without specialized adaxial prophylls; phyllotaxis is initiated by two foliage leaves; third foliage leaf present or absent. There are two or three cataphylls on lateral shoots. Foliage leaves 4–13 mm long, attached to about 1/2 of circumference of a stem; sheath open, up to 1.5 mm long, with membranous margins bearing 3–6 hairs on distal half of each margin, distal most hairs the longest, up to 1 mm; auricles and ligule absent; lamina green, incurved backwards to straight, with single vascular bundle, rounded in cross-section, 0.2–0.3 mm in diameter, glabrous, apically with a mucro 0.05–0.15 mm long. Cataphylls not vascularized, membranous, in form of open sheaths. Cataphylls of each shoot are successively longer ( Fig. 2B ); proximal one(s) 1–3 mm long, margins not overlapping, apex acute or obtuse; the uppermost and the longest one 3.5–5 mm long, enrolled into a tubular structure 0.4–0.5 mm in diameter enclosing basal part of a scape, with margins overlapping but free. One to four upper cataphylls (sometimes both, if there are only two of them) possess a compact group of hairs 0.4–0.5 mm long on subapical part of abaxial surface ( Fig. 2B,C ). Scape ( Fig. 2A ) erect, terete, glabrous, up to 50 mm long, basally filiform and ca. 0.1 mm in diameter, in the upper third much thicker, 0.4–0.5 mm in diameter. Development and anthesis of inflorescences on shoots of different order is sequential, so that different developmental stages can be found on a given plant. Elongation of the scape takes place shortly before anthesis. Primary inflorescence axis with two subopposite primary bracts. The lower primary bract ( Fig. 3A ) erect, 2.8–4.7 mm long, glabrous, not papillose; base completely encircles the inflorescence axis; sheath laterally compressed, with 5 vascular bundles, central part indurated with membranous margins apically prolonged into 0.1–0.3 mm long auricles; lamina 0.7–1.7 mm long (c. 1/5–1/4 as long as the sheath), terete, apically with a minute mucro. The upper primary bract ( Fig. 3B ) inserted immediately above the lower primary bract, sheath 2.5–4.6 mm long, not reaching to just slightly exceeding the sheath of the lower one; base completely encircles the inflorescence axis, cucullate, the sheath midline strongly curved from the base and sometimes distinctly produced at the base containing the spikelet, such that the two primary bracts are distinctly asymmetric in outline, sheath with 3 vascular bundles, with smooth central part and papillose membranous margins prolonged into auricles up to 0.3 mm long; lamina about as long as the auricles, terete, shorter than lamina of lower primary bract. Lateral spikelet one, in axil of the upper primary bract, hidden by closed sheaths of both the lower and the upper primary bracts, except for exposed stigmas. Spikelet dorsiventral, with distichous arrangement of 4–5 flowers. All flowers bisexual, each associated with two tepal-like phyllomes ( Fig. 3C–E ). Phyllome 1 glabrous, not papillose, 0.1–0.2 mm wide and 0.04–0.08 mm long, entire or bilobed. Phyllome 2 completely membranous, glabrous, not papillose, not vascularized, folded to enclose young stamen and carpels, 2.0– 3.2 mm long, 0.5–0.7 mm wide, margins entire, apex acute to obtuse, denticulate-erose. Stamen 1, on the radius of tepal-like phyllome 2, filament basally for a very short distance fused to gynoecium, anther 0.8–0.9 mm long. Carpels (4–)6–7(8), longitudinally dehiscent at fruit maturity. Gynophore ca. 0.1 mm long. Styles 1 per carpel, basally adnate to the gynoecium and to other styles. Stigmas with 3–5-cellular papillae ca. 0.07 mm long in two rows along ventral side. Seeds c. 0.5 mm long, red-brown, with inconspicuous ornamentation of low ridges.

Diagnosis and relationships:— The presence of up to four cataphylls and the presence of one long and one short phyllome associated with each flower apparently distinguish C. milleri from all other species of the genus. In habit ( Fig. 1D ), C. milleri superficially resembles C. drummondiana (to which it is not closely related), but differs from it in the presence of two to five cataphylls (vs. one in C. drummondiana ) at the base of a scape, in the shortened (vs. up to 2 mm long) internode on the inflorescence axis between the two primary bracts, in the dimorphic (vs. monomorphic) morphology of the primary bracts and in the presence of one long and one short (vs. two long and one short) tepal-like phyllome associated with each flower. The absence of a spikelet in the axil of the lower primary bract and the dimorphic nature of the primary bracts are shared with species such as C. polygyna ( Brown 1810: 253) Hieronymus (1873: 210) and C. glabra (von Mueller ex Sonder 1856: 226) Hieronymus (1873: 209) , to which C. milleri is apparently related. Another potentially related species is C. mutica ( Brown 1810: 253) Hieronymus (1873: 211) because of the reported presence of up to two (vs. one as in most spp. of Centrolepis ) cataphylls ( Cooke 1992), the similarly asymmetric primary bracts, and the suppression of the spikelet in the axil of the lower primary bract in some C. mutica inflorescences (lower spikelets can be present or absent in C. mutica ). Centrolepis milleri differs from C. mutica in possessing a prominent tepal-like phyllome associated with each anthetic flower (absent in C. mutica ), and entire margins of primary bracts (margin of lower primary bract is ciliolate in C. mutica , see Cooke 1992).

Since as C. milleri superficially resembles C. drummondiana and the two species sometimes grow together at a single locality, we have checked type material of C. drummondiana and its synonyms listed by Cooke (1992). A list of examined type material is provided below. All these specimens sufficiently differ from C. milleri .

Centrolepis drummondiana = Devauxia drummondiana Nees von Esenbeck 1841: 51 ; type: Swan river, Drummond s.n. –B!) do not belong to the taxon described here as C. milleri . These synonyms are:

Devauxia (‘Desvauxia’) brevifolia Nees von Esenbeck (1846: 70) , type: In rupestribus umbrosis sumitatis montis Clarence (Plantagenet), 31 Sept. 1840, Preiss 1749 (B!).

Devauxia (‘Desvauxia’) urvillei Steudel (1855: 267) , type: Port du Roi Georges, 1826, D. D’Urville 1328 (P– photo!).

Centrolepis pulchra Hieronymus (1873: 213) , type: Nov. Hollandia austr. occid., c. 1844, Drummond 930 (B!).

Phenology: — Spring flowering (probably August–November); in the wild plants observed in seed during October, cultivated plants flowered November–December in Perth, Western Australia.

Distribution and Ecology:— Endemic to south-western Australia, where it is restricted to sandplains in 2 disjunct areas: (1) the Eneabba sandplain on the southern end of the Geraldton Sandplains Bioregion (IBRA7, http://www. environment.gov.au/topics/land/national-reserve-system/science-maps-and-data/australias-bioregions-ibra/australias [accessed 14 July 2014]), where it is known from five populations in an area c. 65 x 10 km, and (2) a single location on the Esperance Sandplain NE of Albany. Grows in white to yellow sand in open areas (e.g., along firebreaks and margins of dirt roads). Recorded as growing with annual herbs or geophytes with annual vegetative parts, including Stylidium calcaratum Brown (1810: 570) , Levenhookia pusilla Brown (1810: 572) , Drosera Linnaeus (1753: 281) spp. , Austrostipa Jacobs & Everett (1996: 582) sp. , and Crassula Linnaeus (1753: 282) spp.

Although apparently not collected until 2003, C. milleri is common at several locations, and possibly extensive through a much larger area than currently known in suitable microhabitat. Specimens of C. milleri grow with their leaves mostly buried by sand. We speculate that this semi-subterranean habit might possibly be an adaptation to avoid light or moisture stress in its environment, but may require quite pure sands to allow some transmitted light, which might partly explain its apparently restricted distribution. Plants in some populations of C. cephaloformis Reader (1902: 97) are likewise buried just below the surface in white sands (and due to the sessile inflorescences can sometimes completely lack emergent parts other than anthers and stigmas).

Conservation status: — Currently listed as Priority Three under Department of Parks and Wildlife Conservation Codes for Western Australian Flora, under the name Centrolepis sp. Eneabba (B.P. Miller s.n. 31/12/2009), Western Australian Herbarium, in FloraBase, http://florabase.dpaw.wa.gov.au [accessed 14 July 2014]. The species is reported to be common at several locations. Parts of the distribution have been cleared, but the species is conserved in the Mt Benia Reserve.

Etymology: — The species epithet honours Dr. Benjamin P. Miller of the Botanic Gardens and Parks Authority, who discovered C. milleri during seed bank audits and brought it to our attention. Dr. Miller has worked for many years on the Eneabba Sandplain , studying plant community and population ecology, including post-fire recruitment studies, during which C. milleri plants were first discovered in 2003.

Additional specimens examined (paratypes): — WESTERN AUSTRALIA: North side of Woolmulla Rd , Eneabba sandplain , B. P. Miller s.n. ( PERTH) ; Cultivated at Kings Park and Botanic Garden ex Eneabba sandplain , 31.xii.2009, B. P. Miller s.n. ( PERTH, MW) ; Drawbin Rd , NNE of Manypeaks, 29.x.2003, E. M. Sandiford 926 ( PERTH) ; loc. cit., 20.x.2003, E. M. Sandiford 997 ( PERTH) ; S of Jurien Rd and E of Black Arrow Rd, 25.ix.2014, M. D. Barrett & D.D. Sokoloff 112 ( MW) .

Figures

FIGURE 1. Habit of Centrolepis milleri (S of Jurien Rd and E of Black Arrow Rd, 25.ix.2014, M.D. Barrett & D.D. Sokoloff 112). A. Plants in natural habitat, with sand blown away from leaves of one plant. B. Detail showing leaves mostly buried by sand. C. Plant removed from the sand. D. Centrolepis drummondiana (left) and C. milleri (right) growing side by side in natural habitat.

FIGURE 2. Habit and cataphylls of Centrolepis milleri, scanning electron microscopy (cultivated at Kings Park and Botanic Garden ex Eneabba sandplain, 31.xii.2009, B.P. Miller s.n.). A. Entire plant with unbranched main shoot. B. Cataphylls at the base of a scape of main shoot of a vigorous plant. C. Cataphyll, abaxial view. Abbreviations: co, cotyledon; hy, hypocotyl; in, inflorescence; l1, l2, l3, foliage leaves numbered sequentially; lr, lateral root; pr, primary root; sc, scape; arrowhead, collar (collar hairs appressed to root/hypocotyl and not conspicuous in this image). Scale bars = 1 mm in A, 300 μm in B, C.

FIGURE 3. Inflorescence and flower morphology of Centrolepis milleri, scanning electron microscopy (cultivated at Kings Park and Botanic Garden ex Eneabba sandplain, 31.xii.2009, B.P. Miller s.n.). A. Preanthetic inflorescence with lower primary bract enclosing all other organs. B. Side view of upper primary bract that encloses a spikelet. C. Flowers as seen when an upper primary bract removed. D. Flower removed from inflorescence, with tepal-like phyllome 2 detached. E. tepal-like phyllome 2, adaxial view. Abbreviations: an, anther; aub, auricles of upper primary bract; llb, lamina of lower primary bract; lub, lamina of upper primary bract; ov, ovary; sc, scape; sf, stamen filament; sg, stigma; slb, sheath of lower primary bract; tlp, tepal-like phyllome 2; arrowhead, tepal-like phyllome 1. Scale bars = 300 μm in A–E.