Homalomeneae (Araceae) of Borneo XXX — Homalomena atlas [Hanneae Complex] a new species from the Rejang Basin, Sarawak

. Homalomena atlas is described and illustrated as a new species from the western Rejang Basin and assigned to the Hanneae Complex of the Cyrtocladon Clade, taking the complex to 12 described species on Borneo.


INTRODUCTION
The Homalomena Hanneae Complex (Ng et al. 2011: 26) of the Cyrtocladon Clade (Wong et al. 2013) is a highly distinctive group of species notable for leaf blades with conspicuous extrafloral nectaries, amber-coloured resin secreted from between the staminate florets shortly before staminate anthesis (Hoe et al. 2011(Hoe et al. , 2016;;Wong & Boyce 2017), and spathes white at anthesis with the persistent post-anthesis spathe turning deep pink to red as the fruits develop.Until recognition of Homalomena electra P.C.Boyce & S.Y.Wong (Boyce & Wong 2017) from Peninsular Malaysia the Hanneae Complex was considered to be entirely Bornean (but see Wong et al. 2013: 592).Including that described here, the complex comprises 13 described species, all except H. electra restricted to Borneo, and with most species localized.Based on field observations and in particular the huge amount of undeterminable material deposited in herbaria the Hanneae Complex is most probably contains well in excess of 100 species Geology in this paper is specified based on Hutchinson (1989Hutchinson ( , 2005) ) and Tate (2001).

Diagnosis
Homalomena atlas is immediately distinguished in the Hanneae Complex by the matte brick-red peduncles with dense pale grey broken longitudinal striations, glossy scarlet petiole bases and dark red petiolar sheath, and by the lower spathe inflating to almost globular during anthesis.Homalomena atlas most nearly approaches H. mutans (with which it co-occurs at the type locality -see Boyce & Wong 2014: 66) and from which it further differs by the interstice between the zones of staminate and pistillate florets being narrower that the adjacent parts of the respective zones (vs interstice markedly swollen to exceed the width of the fertile zones), and by the glossy broadly ovate-cordate (vs matte triangularcordate) leaf blades Description Medium-sized, rather robust, evergreen, glabrous clumping herb to c. 1 m tall.Crushed tissues strongly aromatic of turpentine.Stem initially erect, decumbent with age with the active tip ascending, 3-3.5 cm thick, semi-glossy medium green; older parts brown; adventitious roots copious, conspicuous, penetrating petiole bases; internodes 1.5-2.5 cm long.Leaves up to ca 20; individual shoot modules beginning with a conspicuous 2-keeled semi-persistent scarlet prophyll; petiole 60-70 cm long × 9-12 mm wide, erect, older leaves with the petiole spreading or procumbent, pulvinate ca 2/3 way along from base, weakly D-shaped in cross-section with angles rounded, distally shallowly canaliculate with the angles bluntly rounded, medium green with broken paler longitudinal striae, lower fifth (about half equal to the length of the sheathing portion), glossy scarlet; petiolar sheath 10-15 cm long, c. 1/5 of petiole length, with wings up to 1 cm wide proximally, tapering distally, open, weakly decurrent at apex, their margins slightly incurved; wings initially deep red brown, soon marcescent along margin, eventually whole sheath marcescent; blade broadly ovato-sagittate or ovato-cordate, 35-45 cm long × 25-35 cm wide, thinly leathery; somewhat quilted between impressed primary veins, with scattered punctate extrafloral nectaries, semi-glossy dark green adaxially, slightly paler abaxially, sagittate at base with sinus narrowly triangular; posterior lobes subtriangular with the outer margin rather abruptly curved, and the inner margin straight to very slightly incurved, obtuse at apex; anterior lobe broadly triangular, acute; midrib raised abaxially, c. 8 mm wide at base, 4 mm wide at centre, adaxially impressed; primary lateral veins c. 20 on each side, diverging at 30-70° from midrib, adaxially impressed, abaxially sharply raised, curved towards apex when near margin; interprimary veins slightly impressed adaxially, slightly raised abaxially, alternating irregularly with primaries, posterior lobes each with 4-6 primary veins; secondary venation abaxially raised, arising from mid-rib and primary and interprimary veins; tertiary venation invisible, all veins running into a slightly thickened intramarginal vein.Blooms usually up to 10 together in a simple synflorescence, erect, smelling of anethole at anthesis, post-anthesis and into fruiting declinate; first bloom subtended by a red prophyll, c. 5 cm long × 1 cm wide; subsequent blooms subtended by slightly shorter red prophylls; peduncle 15-18 cm long × 5.0-7.5 mm wide, matte brick red with very numerous pale grey broken longitudinal striae.Spathe c. 11 cm long × ca 4 cm wide; lower spathe inflating globose and spathe limb loosening at pistillate anthesis, spathe limb opening widely cucullate at staminate anthesis, white, dorsally with a yellow-pale green median band corresponding to mid-keel and flanked by two paler similarly coloured bands, middle band becoming brick red where it runs into the peduncle, 2.5 cm long × c. 2.5 cm wide, spathe strongly constricted with constriction coinciding with the base of the staminate floret zone; spathe limb c. 7 cm long × c. 4 cm wide at pistillate anthesis, ovato-triangular, with greenish red-tipped terminal mucro to c. 3 mm.Spadix 12-12.5 cm long at anthesis, stipitate, spadix shorter than spathe at onset of anthesis, then rapidly extending and bending forwards during pistillate anthesis until exceeding spathe limb by c. 1 cm; stipe c. 10 mm long × c. 53 mm wide, cylindrical, inserted obliquely on peduncle, waxy white; pistillate floret zone c. 4 cm long × 1.5 cm wide, c. 1/3 length of spadix, slightly fusiform, very pale yellow; pistils 1.5-2 mm in diameter, c. 1.5 mm tall, globose-cylindrical, crowded, yellowish; infrapistillar staminodes mostly one per pistil, (rarely two or staminodes in basal-most florets); stipitate with a globose head 0.8-1 mm in diameter, not quite equalling pistils in height, waxy white; style barely differentiated; stigma globose-capitate, about as wide as ovary, dirty white, wet at anthesis; sterile interstice tapering and narrower than the adjacent fertile zones, with 2-3 rows of hardly individually distinguishable rhomboidal ivory staminodes; staminate floret zone 7-8 cm long × c. 1 cm wide at staminate anthesis, c. 2/3 length of spadix, cylindrical, tapering basally; amber droplets of resin secreted from between staminate florets prior to onset of staminate anthesis; staminate florets polygonal in plan view, 2.0-3 mm in diameter, each comprising 4(-6) truncate stamens each overtopped by large and flat connective tissue, ivory white; pollen in short strings, white, forming a paste when mixed with resin.Infructescences up to  10 together, declinate to pendent; spathe entirely persistent, deep red; peduncle matte dark brick red conspicuous striae; fruits not observed.

Eponymy
From Atlas, a Titan in Greek mythology condemned to hold up the heavens for eternity following the conflict between the Titans and the Olympians.In artistic depictions Atlas is portrayed supporting a celestial sphere on his shoulders.The name is coined in allusion to the globose lower spathe.

Distribution
Sarawak, restricted to the western Rejang basin, with the populations occurring as far east as the confluence of the Rejang and Balleh rivers.

Figure 2 .
Figure 2. Homalomena atlas S.Y.Wong & P.C.Boyce.A. Emerging blooms B. Detail of peduncle.C. Junction of peduncle and lower spathe.D & E. Front and rear views of a bloom at late pistillate anthesis.See description for dimensions.
Homalomena atlas forms extensive patches, occasionally intermixed with Homalomena mutans P.C.Boyce & S.Y.Wong and H. ibanorum S.Y.Wong & P.C. Boyce, on open areas of the floor of humid to per-humid lowland dipterocarp forest over shales at between 50 and 100 m.Notes The twelve described Bornean species of the Hanneae Complex are as follows, listed by their occurrence from west to east: Homalomena debilicrista Y.C.