Thuranthos C.H.Wright, 1916

Martínez-Azorín, Mario, Crespo, Manuel B., Alonso-Vargas, María Ángeles, Pinter, Michael, Crouch, Neil R., Dold, Anthony P., Mucina, Ladislav, Pfosser, Martin & Wetschnig, Wolfgang, 2023, A generic monograph of the Hyacinthaceae subfamily Urgineoideae, Phytotaxa 610 (1), pp. 1-143 : 104-106

24. Thuranthos C.H.Wright

in Bull. Misc. Inform. Kew 1916(9): 233 (1916) ( Figs 60 , 61 ).

Typus generis:— T. macranthum (Baker) C.H.Wright (holotype).

≡ Drimia sect. Thuranthos (C.H.Wright) J.C.Manning & Goldblatt in Strelitzia 40: 62 (2018) pro parte. Typus sectionis:— D. macrantha (Baker) Baker (holotype).

Description:—Medium to tall bulbous geophyte. Bulb hypogeal, ovoid to subglobose, 3‒15 cm in diam., with white, fleshy, spathulate and commonly pediculate, loose scales. Roots thickened and branched. Leaves 2‒7(‒14) per bulb, hysteranthous, 10‒70 cm long, narrowly linear, channelled and usually keeled, green, sometimes basally maculate, somewhat glaucous, smooth, glabrous. Inflorescence a lax, erect raceme, 15‒50 cm long, with 3–40 flowers; peduncle 30‒150 cm long, erect, terete, smooth; pedicels (10–) 30‒70 mm long, subpatent and arching downwards distally at anthesis, erect in fruit. Bracts ovate-lanceolate, 3‒10 mm long, lowermost with distinct spur, early caducous at flowering and leaving a distinct scar; bracteoles present and evident, also early caducous. Flowers stellate with strongly reflexed tepals at full anthesis, nodding, nocturnal, opening in late evening and closing before sunrise, fragrant during night. Tepals 6, biseriate, (10‒) 15‒37 mm long, narrowly oblong, obtuse, yellow, brown, carneous or whitish with darker brownish-greenish longitudinal band more evident on abaxial side, almost free to very shortly connate for 1‒2 mm. Stamens 6, erect, sigmoid, yellow, brown to white or cream colour; filaments 7‒20 mm long, linear, flattened and expanded below and incurved, leaving opening among them to show ovary, connivent to style at upper half/third, and slightly spreading distally and commonly pale in colour, adnate to tepals at base; anthers oblong, 2‒7 mm long, basifixed, yellow, orange or green, with yellow or white pollen. Ovary ovate to conical, 4.0‒ 6.5 mm long, greenish. Style 7‒22 mm long, erect, white, columnar, ending in small or distinctly capitate, thickened stigma. Capsule ovate to oblong or ellipsoid, trigonous, deeply 3-lobed, 10‒50 mm long, pale brown, valves completely dehiscing from base, tepals cohering and inrolled above ovary after anthesis, circumcissile from base and persisting as a cap at the top of the developing capsules. Seeds ellipsoidal to broadly ellipsoid, flattened, 6‒16 mm long, testa black, glossy, with slightly sinuous anticlinal cell walls.

Number of species and distribution:— Thuranthos includes eight species mostly confined to Southern Africa and East Africa, being in the Uzambara-Zululand Region and the Southern and Eastern Sections of the Zambezian Subregion, with a species occurring in the Karoo‐Namib Region (sensu Takhtajan 1986 and Martínez-Azorín et al. 2023a), ( Fig. 49 ). For further species characterisation see Dyer (1964), Stirton (1976), Obermeyer (1980c), Stedje (1987), Speta (1998a), Newton (2003), and Manning & Goldblatt (2018).

Karyology:—2n=20 ( De Wet 1957, as Thuranthos macranthum (Baker) C.H.Wright ); 2n=20+4B ( Stedje 1996 as Drimia macrocarpa Stedje ).

History, diagnostic characters, and taxonomic relationships:— Wright (1916) described Thuranthos based on a distinct species with a remarkable, unique flower morphology within Urgineoideae at that time, showing nocturnal, large, nodding flowers with filaments that Stirton (1976) considered an outstanding feature showing flattened, convex basal regions that are connivent to the style at the middle and spread above, resembling a paper lantern with longitudinal slits ( Figs 60 , 61 ). Speta (1998a) accepted this genus based on its evident morphological differentiation from other urgineoids. This genus was characterised by the imbricate, loose bulb scales; keeled, proteranthous leaves; the presence of bracteoles; the nodding, nocturnal flowers with the peculiar morphology of filaments described above, the erect style and the large, flat, ovate seeds.

The phylogenetic study of Martínez-Azorín et al. (2023a) included six samples of Thuranthos macranthum , T. nocturnale Dyer (1964 : t. 1439), and T. pauciflorum ( Baker 1892: 6) Martínez-Azorín et al. (2019a: 295) , the latter including T. basuticum ( Phillips 1917: 306) Obermeyer (1980c: 139) in synonymy (see Martínez-Azorín et al. 2019a). This is a genus restricted to Southern Africa and East Africa, and one which formed a strongly supported clade included in a polytomy with the monophyletic and well supported Ledurgia and Zingela . Martínez-Azorín et al. (2023a) considered Thuranthos to resemble Vera-duthiea on account of the nodding, nocturnal flowers with filaments usually approaching the style at the middle, but differing in the style, which is distinctly deflexed, the spotted, not keeled leaves, the lack of bracteoles [except in V. macrocarpa (Stedje 1987: 664) Speta (2016: 155) ], and in their different phylogenetic relationships, as it is sister to Ebertia ( Martínez-Azorín et al. 2023a) . Our recent unpublished phylogenetic analyses of samples of Drimia macrocarpa Stedje (1987: 664) from Mapanza Mission in Zambia (Robinson 316 K! number H.212/95 90; seeds kindly provided by Royal Botanic Gardens, Kew), show its close relation to Thuranthos instead of Vera-duthiea . This recent finding facilitates the refinement of the circumscription of the latter two genera and therefore, Thuranthos is expanded to include the species with loose bulb scales, nodding, nocturnal flowers with basally expanded filaments that are sigmoid and connivent to the style along the middle portion and spreading above and presence of bracteoles and Vera-duthiea , including species with compact bulb scales, absence of bracteoles and filaments narrow and contracted at the joint to tepals, among other characters. This new circumscription of the two genera eliminates the exception of the presence of bracteoles and loose bulb scales in D. macrocarpa when included in Vera-duthiea by Speta (2001, 2016) and Martínez-Azorín et al. (2018b, 2023a).

Samples of Zingela consistently form a well‐supported clade sharing with Thuranthos the loose bulb scales; hysteranthous leaves and presence of bracteoles; however, Zingela differs by the diurnal flowers and filiform, spreading stamens with circinnate dehisced anthers ( Crouch et al. 2018), and are placed in a polytomy with Thuranthos and Ledurgia ( Fig. 2 in Martínez-Azorín et al. 2023a), which is resolved in the parsimony analyses ( Figs S5 , S 7 in Martínez-Azorín et al. 2023a) where Ledurgia and Zingela form sister clades.

Therefore, we accept Thuranthos as a distinct genus following Stirton (1976), Obermeyer (1980c) and Speta (1998a), though with the necessary recircumscription.

Manning & Goldblat (2018) accept D. sect. Thuranthos to include five species from Southern Africa: D. macrantha , D. basutica , D. vespertina (a newly described species from northern Namibia and southern Angola), D. hesperantha (= Urginea revoluta ), and D. indica . As reported by Martínez-Azorín et al. (2018b), Drimia indica belongs to Indurgia , a genus restricted to India and neigbouring countries, and plants identified as D. indica in South Africa were recently described as Vera-duthiea zebrina Martínez-Azorín et al. (2018b: 285) and Zingela pooleyorum Crouch et al. (2018: 36) . Similarly, D. vespertina seems to better fit the concept of Thuranthos of this work based on flower morphology and the expanded filaments, though the compact bulb scales, the absence of bracteoles, the general small plant size and its distribution makes its inclusion in the genus deviant. Further studies are needed to ascertain its phylogenetic relationships. Finally, Urginea revoluta is excluded from Thuranthos based on flower and seed morphology and our phylogenetic results ( Martínez-Azorín et al. 2023a).

Accepted species and required new combination and new name:—

Figures

FIGURE 2. Seed morphology in Urgineoideae. 1. Drimia neriniformis Baker; 2. Drimia robusta Baker; 3. Fusifilum capitatum (Hook.) Speta; 4. Fusifilum montanum (A.P.Dold & E.Brink) A.P.Dold et al.; 5. Fusifilum physodes (Jacq.) Speta; 6. Geschollia anomala (Baker) Speta; 7. Geschollia brachyandra Mart.-Azorín et al.; 8. Geschollia calcarata (Baker) Mart.-Azorín et al.; 9. Geschollia globuligera Mart.- Azorín et al.; 10. Geschollia occultans (G.Will.) Mart.-Azorín et al.; 11. Geschollia prolifera Mart.-Azorín et al.; 12. Indurgia congesta (Wight) Speta; 13. Indurgia indica (Roxb.) Speta; 14. Iosanthus amboensis (Baker) Mart.-Azorín et al.; 15. Iosanthus macrostigma Mart.-Azorín et al.; 16. Iosanthus toxicarius (C.Archer & R.H.Archer) Mart.-Azorín et al.; 17. Litanthus pusillus Harv.; 18. Litanthus stenocarpus (J.C.Manning & J.M.J.Deacon) Mart.-Azorín et al.; 19. Mucinaea nana (Snijman) M.Pinter et al.; 20. Rhadamanthopsis haworthioides (Baker) Mart.-Azorín et al. All to the same scale in mm.

FIGURE 5. Seed morphology in Urgineoideae. 1. Tenicroa multifolia (G.J.Lewis) Oberm.; 2. Tenicroa polyantha M.Pinter et al.; 3. Tenicroa unifolia (A.V.Duthie) M.Pinter et al.; 4. Thuranthos bakeri Mart.-Azorín et al.; 5. Thuranthos macrocarpum (Stedje) Speta; 6. Thuranthos nocturnale R.A.Dyer; 7. Thuranthos pauciflorum (Baker) Mart.-Azorín et al.; 8. Triandra pellabergensis Mart.-Azorín et al.; 9. Urginavia altissima (L.f.) Speta; 10. Urginavia capensis (Burm.f.) Mart.-Azorín et al.; 11. Urginavia echinostachya (Baker) Mart.-Azorín et al.; 12. Urginavia kniphofioides (Baker) Mart.-Azorín et al.; 13. Urginavia micrantha (A.Rich.) Speta; 14. Urginavia multisetosa (Baker) Mart.-Azorín et al.; 15. Urginavia simensis (Hochst. ex A.Rich.) Mart.-Azorín et al.; 16. Urginea fugax (Moris) Steinh.; 17. Urgineopsis arenosa (Adamson) Mart.-Azorín et al.; 18. Urgineopsis dregei (Baker) Mart.-Azorín et al.; 19. Urgineopsis exilis (Adamson) Mart.-Azorín et al.; 20. Urgineopsis gracilis (A.V.Duthie) Mart.-Azorín et al. All to the same scale in mm.

FIGURE 7. Aulostemon mzimvubuensis (van Jaarsv.) Mart.-Azorín et al.

FIGURE 49. Approximate distribution ranges of accepted genera in Urgineoideae.

FIGURE 60. Species of Thuranthos C.H.Wright displayed in horizontal rows of images. 1. Thuranthos macranthum (Baker) C.H.Wright from Wright (1916: t. 8680); 2. Thuranthos nocturnale R.A.Dyer from Dyer (1964: t. 1439).

FIGURE 61. Species of Thuranthos C.H.Wright displayed in horizontal rows of images. 1. Thuranthos bakeri Mart.-Azorín et al.; 2. Thuranthos macranthum (Baker) C.H.Wright; 3. Thuranthos macrocarpum (Stedje) Speta (Photographs of flowers by B. Stedje); 4. Thuranthos nocturnale R.A.Dyer; 5. Thuranthos pauciflorum (Baker) Mart.-Azorín et al.