Helonias leucantha (Koidz.) Tanaka (1998a: 107)

Tanaka, Noriyuki, 2019, Taxonomy, evolution and phylogeography of the genus Helonias (Melanthiaceae) revisited, Phytotaxa 390 (1), pp. 448-450 : 448-450

8. Helonias leucantha (Koidz.) Tanaka (1998a: 107) ( Figs. 18–20 ).

≡ Sugerokia leucantha Koidzumi (1937: 46) . Type:― JAPAN. Loochoo [Ryûkyû, Okinawa Pref. ]. Insula Utchina [Okinawa I.]; Kunchan, Hetona, Abagawa, Yonagawa, Katena, Taniwadake, Ajagawa, T. Sonohara (Syntype in KYO; photo of a syntype from Abagawa in TNS-320909!). ≡ Heloniopsis leucantha Koidzumi (1937: 46) . ≡ Hexonix leucantha (Koidz.) Wang & Tang (1949: 114) .

Japanese name:―Ô-shiro-shôjôbakama ( Koidzumi 1937).

Description:―Rhizome subcylindrical, stout, to 2 cm long, 1.5 cm in diam. Roots filiform, ca. 1 mm in diam., white. Leaves persistent for 1–2 years, narrowly oblanceolate or spatulate, 10–31 cm long, 2–4 cm wide, base cuneate, apex acuminate or acute, with apiculus 0.7–2 mm long, somewhat thick in texture, glossy, abaxial midvein slightly raised, adaxially veins indistinct. Flowering stem to 27 cm long (incl. inflorescence); peduncle fistular, 5–25 cm long, 3–8 mm in diam. in middle, light green; scale-like leaves on peduncle usually 5–12 (excl. basal ones), narrowly lanceolate or subulate, to 3.8 cm long, becoming smaller upward, acute, involute, whitish or pale green, submembranous; inflorescence a short compact raceme, rachis to ca. 3.5 cm long, often slightly drooping distally; pedicels decurved at anthesis, 6-ribbed, to 11 mm long at anthesis, to 20 mm long in fruit, white, ebracteate. Flowers 4–36, often secund, nodding, (tubular-)campanulate, odorless or sometimes faintly fragrant, protogynous. Tepals 6, narrowly oblong or narrowly elliptic-oblong, 9.5–16.5 mm long, 2–6.5 mm wide, apex acute, recurved distally, silky white, sometimes pale lilaceous, turning pale pink with progression of anthesis, adaxially canaliculate toward base, proximal submarginal portions raised, proximal margins narrowly and slightly revolute, often slightly imbricate, basal nectary saccate adaxially; abaxial base slightly gibbous; base of tepal affixed to receptacle (apex of pedicel) for ca. 1–1.2 mm in length. Stamens 6, usually exserted beyond tepals; filaments from adaxial rim of nectary of opposing tepal, filiform-subulate, 4.4–18.5 mm long, base slightly dilated and complanate, white or pale lilaceous; anthers narrowly ovoid or ellipsoid, 1–2.5(–3.3) mm long, base sagittate, apex obtuse, virtually bilocular, with vestigial apical confluence between thecae, basifixed adaxially, extrorse, pale to dark (bluish) purple; pollen whitish. Pistil 1, usually exceeding stamens and tepals; ovary globose or obovoid, slightly trilobed, 2.5–3 mm long, 3–3.7 mm across, apex emarginate-concave, yellowish green, dull dark purple, or dull dark purplish green, often with short stipe (gynophore) to 0.6 mm long; style terete, strict, 4.5–14.5 mm long, pale purple or purplish pink; stigma densely papillulate, discoid, depressed capitate or hemispheric, often obtusely trigonous or slightly trilobed, 1.3–2.2 mm across, 0.7–1.2 mm thick, white, light purple or dark purplish pink; ovules numerous, multiseriate on central axile placentae. Capsules obpyramidal, obcordate in lateral aspect, apex depressed in center, tripartite, 8–9 mm long, 8–12 mm across, lobes mitriform, divergently protruding subdistally. Seeds sublinear or narrowly fusiform, testa whitish, proximally caudate, distally acicular, 4.5–5.8 mm long, 0.25–0.3 mm wide; body of seed oblong-fusiform, 1–1.5 mm long, 0.2 mm wide, (dark) brown.

Additional specimens examined (see also Tanaka 1998a):― JAPAN. Okinawa. Okinawa Pref. Okinawa Isl. : Kunigami-gun, Ôgimi-son, 16 August 1951, T. Amano 6331 (TNS-129705); Haneji-son, Makiya-ku, 29 November 1954, M. Nakamine 322 (RYU-41828; TNS-116547, 116548). Iriomote Isl.: Urauchi Riv., 150 m, 13 June 1971, T. Yamazaki (TI). Ishigaki Isl.: August 1958, Y. Niiro (RYU-19301).

Distribution:―SW Japan, Nansei Islands (incl. Ryûkyû Isl.). Kagoshima Pref.: Tokunoshima Isl. ( Hatusima 1986). Okinawa Pref. : N Okinawa, Ishigaki, and Iriomote Isl. ( Fig. 29-L ).

Habitat:―Shady moist rocks and slopes near or along streams in forests at elevations 120–400 m.

Conservation status:―Assessed by the Environment Agency of Japan (2000) as EN on the basis of the criterion E in IUCN (1994). Deforestation and dam construction are regarded as main threats to the species.

Flowering:―Late December–mid March.

Ripening:―April–May.

Remarks:― Helonias leucantha is most closely allied to H. umbellata (e.g. Figs. 21 , 22 ), from which it differs by its usually larger leaves ( Fig. 18D ), nodding tubular-campanulate flowers ( Figs. 18A–D , 19A ), narrowly oblong-elliptic tepals imbricate proximally ( Figs. 19A, D ), and somewhat smaller anthers ( Fig. 19A, D ). The tepals are usually white, but turn pale pink or purplish pink as flowering proceeds. Flowering of Helonias leucantha slightly precedes ser. Heloniopsis , and this may be due to the warm, maritime climate of the Nansei Islands where it occurs. Cernuous, campanulate, often scarcely fragrant flowers of Helonias leucantha are supposed to have originated in response to pollinators ( Tanaka 1997d).

Figures

FIGURE 18. Helonias leucantha. A, B, E–G: material L-4. C, D: L-2. A. Flowering plant (photo on 24 January 2015). B. Raceme from plant in A (24 January 2015). C. Young slightly open flowers with protruding stigmas (21 January 2013). D. Raceme of pale purplish pink flowers (3 February 2013). E. Infructescence with dehiscing capsules (30 April 2012). F. Rosette with flower bud (long arrow) and sprouting small fresh leaves (short arrow) (19 December 2014). G. Plant with fresh green leaves and yellowish leaves developed in preceding year (arrowed) (14 August 2014).All photos at Hachioji, Tokyo.

FIGURE 19. Helonias leucantha. A. Flower (material L-1). B. Proximal interior of flower with frontal tepals and stamens removed (L- 3). C. Vertical section of flower (L-1). D. Interior of partial flower (L-1). E. Proximal interior of partial flower (L-2). IF; inner filament. Scale at B also for C.

FIGURE 20. Helonias leucantha. A. Proximal part of flower, cross section (L-2). B. Proximal part of flower with ovary removed, cross section (L-2). C. Indehiscent anthers with rudimentary apical confluence between thecae (arrowed) (L-2). D. Distal part of pistil and dehisced anthers with rudimentary apical confluence between thecae (arrowed) (L-2). E. Dehiscing capsule with persistent floral parts (L-4). F. Seeds (L-4). OF; outer filament. OVB; base of ovary. Scale at A also for C and D.

FIGURE 21. Helonias umbellata. A. Young slightly open flowers with protruding pistils (material U-1; photo on 3 March 1989). B. Flowering plant (U-2; 14 March 1989). C. Umbel (U-1; 30 March 1992). D. Plant with fresh leaves (light green) and leaves developed in preceding year (darker green) grown in greenhouse during winter (U-3; 14 March 2015). All photos at Hachioji, Tokyo.

FIGURE 22. Helonias umbellata. A–E: material U-1. F: U-4 (in spirit). A. Flower with two frontal tepals and stamens removed. B. Closeup of proximal interior of flower. C. Vertical section of flower with ovary shortly stipitate at base. D. Proximal interior of partial flower. Minutely connate portions between adjoining tepals arrowed. E. Proximal part of flower in cross section. F. Distal part of flower with anthers showing apical confluence between thecae (arrowed). Scale at B also for C–E.

FIGURE29.Distributionofsixspeciesbelongingtotwoseriesofsubsect.HeloniopsisinEAsia.B:Heloniasbreviscapa.Ka:H.kawanoi.Ko: H.koreana.L:H.leucantha.O:H.orientalis.U:H.umbellata.Ser.UmbellataecomprisesKa,LandU.Ser.HeloniopsisconsistsofB,KoandO.