Iosanthus Mart.-Azorín, M.B.Crespo, M.Pinter, Slade & Wetschnig

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 : 56-59

10. Iosanthus Mart.-Azorín, M.B.Crespo, M.Pinter, Slade & Wetschnig

in Pl. Biosystems 153(4): 584 (2019; on line 18 December 2018) ( Figs 30–32 ). Typus generis:— I. toxicarius (C.Archer & R.H.Archer) Mart. -Azorín, M.B.Crespo, M.Pinter, Slade & Wetschnig (holotype).

= Drimia sect. Khubusia J.C.Manning & Goldblatt in Strelitzia 40: 120 (2018). Typus sectionis:— D. khubusensis P.C.van Wyk & J.C.Manning (holotype).

Description:—Small to medium deciduous bulbous geophyte, to 50 cm high. Bulb hypogeal, usually solitary or growing in small groups, ovoid to subglobose, 1–3 cm in diam., extended into a 2–5 cm long hypogeal neck, inner scales compact, white, fleshy, outer tunics pale brown-grey, membranous. Roots thickened and branched. Leaves hysteranthous or sometimes synanthous, suberect, spreading and somewhat curved or twisted, 3–16 per bulb, narrowly linear, filiform, 5–18 cm long, subterete to canaliculate, green, sometimes maculate on lower portions, smooth, sometimes surrounded by papery cataphylls. Inflorescence racemose, dense, subcapitate-ovoid or lax and elongated, 0.5–16.0 cm long, with 4–20 flowers; peduncle erect, 1–20 cm long, glabrous; pedicels 1.5–25.0 mm long at anthesis, from suberect to patent and arching downwards; bracts small, 1–2 mm long, membranous, triangular, with slight curve outgrowth or short spur to 1 mm long. Bracteoles absent. Flowers stellate or cylindrical-campanulate, patent to nodding, with suberect to patent-reflexed tepals, diurnal or vespertine-nocturnal. Tepals 6, biseriate, 4–15 mm long, ovate to narrowly oblong and elongated, free or only shortly connate at base, whitish or carneous with central longitudinal pinkish-brown or reddish longitudinal band, straight and spreading or connivent and erect along basal half and spreading patent along apical half. Stamens 6; filaments filiform and subterete or triangular-lanceolate and flat, 1.5–6.0 mm long, adnate to perigone segments at base for 0.5–6.0 mm, erect and connivent to gynoecium or only spreading distally; anthers yellow, ovate-oblong, 1.2–3.0 mm long, basifixed or medifixed, dehiscing longitudinally along their whole length, with yellow pollen. Ovary green, ovoid to conical, trigonous, 2–4 mm long. Style white, erect, 1–7 mm long. Stigma small or distinctly capitate and 3-lobed puberulous. Capsule ovoid to subglobose, 6–15 mm long, erect, dark or pale coloured before dehiscence, with remains of perigone circumscissile below and forming an apical cap, valves splitting to base and usually widely spreading to reflexed. Seeds elliptic to discoid, flattened, broadly winged, with emarginate hilum, 4–10 mm long, testa black to cream-coloured to pale greyish, with sinuous anticlinal cell walls.

Number of species and distribution:— Iosanthus includes 4 species confined to the western regions of Southern Africa, mostly in Namibia and northern South Africa ( Fig. 29 ), hence restricted to the Karoo-Namib Region (sensu Takhtajan 1986). For further information on Iosanthus species see Archer & Archer (1999), Manning & Goldblatt (2018), and Martínez-Azorín et al. (2019c).

Karyology:—Apparently not studied yet ( Goldblatt et al. 2012).

History, diagnostic characters, and taxonomic relationships:— Ornithogalum toxicarium Archer & Archer (1999: 431) was described to accommodate a toxic plant causing severe stock losses in South Africa and Namibia, even though it was earlier determined in scheda as an undescribed species of Urginea . Martínez-Azorín et al. (2019c) presented evidence that O. toxicarium belongs to Urgineoideae and described the genus Iosanthus , as a new and independent phylogenetic lineage within the Urgineoideae ( Martínez-Azorín et al. 2023a) . This new monotypic genus was characterised by the small plant size, filiform leaves, very short peduncle with few-flowers and short raceme, lack of bracteoles, a conical ovary with short tapering style, capsule capped with the withered perigone, and the flattened, ovate, winged seeds.

Manning & Goldblatt (2018) described Drimia khubusensis P.C.van Wyk & J.C.Manning in Manning & Goldbatt (2018: 120) from northwestern South Africa, near the border with Namibia. The species approaches I. toxicarius in several respects, but differs by its elongated and reflexed tepals, and longer and filiform filaments and style. Drimia khubusensis seems to be unique in Urgineoideae in having dark coloured capsules (sometimes blackish), with the valves reflexed from the base at dehiscence to completely expose the creamy-white or pale greyish, flattened, discoid and winged seeds ( Manning & Goldblatt 2018).

The phylogenetic results of Martínez-Azorín et al. (2023a) revealed a perfectly supported clade (Bayesian analyses) corresponding to Iosanthus , including two samples of D. khubusensis sister to a sample of I. toxicarius . Accordingly, the sister is a sample of an undescribed species from Central Namibia, described here as Iosanthus macrostigma Mart. - Azorín et al.; all relationships have strong support. The Iosanthus clade is sister to Indurgia in the combined plastid and nuclear analyses although in the plastidial analyses the former is included in a polytomy related to Indurgia , Urginea , Ebertia , and Vera-duthiea , among others. However, the ML analyses show the undescribed Iosanthus species from Namibia in a polytomy within a wide clade with other related genera like Urginea , Indurgia , and Vera-duthiea among others, although the remaining two described species are placed together in a strongly supported clade. These three Iosanthus species characteristically share a relatively small plant size, hypogeal, compact bulbs, filiform leaves, lack of bracteoles, short and few-flowered inflorescence, and free tepals. We have observed that I. toxicarius also shows dark coloured capsules before their ripening, with valves splitting widely to expose seeds of similar morphology to those of D. khubusensis . These propagules have a prominent endosperm and pale marginal regions in the testa. Further, I. macrostigma from Central Namibia approaches D. khubusensis in leaf, flower, capsule, and seed morphology, although differing in its adnate filaments, which arise from the basal third of the tepals, and in its strongly thickened, capitate, 3-lobed and papillose stigma, among other characters.

Recent phylogenetic and morphological studies on Urginea amboensis from the farm Vergenoeg in northern Namibia collected by A. Eichhoff support its close relationships to I. macrostigma . We, therefore, propose accepting Iosanthus to include the latter four species, which are geographically related and characterised by: small to medium overall plant size; compact, hypogeal bulb with elongated neck; filiform leaves, commonly twisted; short to elongated inflorescence; lack of bracteoles; diurnal or vespertine-nocturnal flowers; capsules with the withered tepals circumscissile below and forming an apical cap, with valves splitting to the base and reflexed; and flattened, ellipsoid, winged seeds with emarginate hilum. Further phylogenetic studies are required to evaluate possible alternatives based on the morphological variation and phylogenetic divergence in the group.

Accepted species and required new combinations:—

Iosanthus amboensis (Baker) Mart. -Azorín, M.B.Crespo & M.Á.Alonso comb. nov. ≡ Urginea amboensis Baker in Bull. Herb. Boissier ser. 2, 3(8): 665 (1903), basionym ≡ Vera-duthiea amboensis (Baker) Mart. - Azorín, M.B.Crespo, M.Pinter & Wetschnig in Phytotaxa 397(4): 296 (2019) ( Figs 2.14 , 30.1 ). Type:— NAMIBIA. Ondangua (1715): Amboland, Ondonga, (–DD), March 1887, Rautanen s.n. (Z000087308! lecto. designated here; Z0001023251! isolecto.).

Comments:— Urginea amboensis Baker (1903: 665) was described from northern Nambia (“Amboland, Ondonga”) and was only known from the type collection by M. Rautanen in March 1887 (Z000087308! and Z0001023251!), which includes inflorescences with closed flowers [resembling those of Dipcadi Medik. (1790: 431) , as seen in posterior identifications] and bulbs, lacking leaves. The protologue indicates that stamens were distinctly shorter than tepals. No further material fitting this species has been found in the studied herbaria, hence precluding its taxonomic placement in the past. Recent taxonomic works placed it as synonym of Drimia indica (Manning & Glodblatt 2018) or as a species of Vera-duthiea ( Martínez-Azorín et al. 2019a) , following the comments by Baker (1903) on its similarity to ‘ U. indica Kunth’.

The study of fresh material recently collected by A. Eichhoff from the farm Vergenoeg in Namibia matches Urginea amboensis Baker (1903: 665) in morphology and distribution. These plants show hypogeal bulbs with compact scales and elongated hypogeal neck; leaves filiform, canaliculate, twisted, green with dark maculae at base; lax, elongated racemes with nodding, nocturnal flowers; tepals free and connivent along the lower half and patent above, filaments adnate to tepals and arising around the middle, erect and connivent to style; bracts minute, deltoid; capsules ovoid elongated and seeds ellipsoid, widely winged with prominent embryo and emarginate hilum ( Figs 2.14 , 30.1 ). These characters approach I. macrostigma , a conclusion supported by our recent unpublished phylogenetic data, in which two samples of U. amboensis from the farm Vergenoeg are placed sister to I. macrostigma with strong support. Samples of the latter two species are sister to a clade combining I. toxicarius and I. khubusense , with the latter relationship being weakly supported in combination in some analyses. Further studies are required to improve our understanding of the group and to evaluate other taxonomic alternatives within the genus.

Iosanthus khubusense (P.C.van Wyk & J.C.Manning) Mart. -Azorín, M.B.Crespo & M.Á.Alonso comb. nov. ≡ Drimia khubusensis P.C.van Wyk & J.C.Manning in Strelitzia 40: 120 (2018), basionym. Type:— SOUTH AFRICA. Northern Cape. Oranjemund (2816): Richtersveld, Khubus [Kuboes], 15 m directly west of first and oldest graveyard, (–BD), 6 October 2014, P.C. V. van Wyk 500 (NBG holo.).

Comments on distribution:—This species was originally described from a single locality in Kuboes (Northern Cape Province of South Africa). The study of the herbarium collection Giess 8270 (WIND!) fits the overall morphology of this species, representing its second locality in the R̂ssingberg, ca. 35 km east of Swakopmund, an extension of ca. 450 km to the north and the first record of the species in Namibia. However, fresh material of the Namibian population is required for final taxonomic placement.

Regarding the collection H. Dauth 160 (WIND!) from near Rosh Pinah in southern Namibia, it also resembles I. khubusense , but clearly differs by the stout peduncle, shorter pedicels (2–3 mm long), and tepals spreading-reflexed from the base, among other characters. It most likely represents an undescribed species in the genus, though further material is needed for its formal description.

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 29. Approximate distribution ranges of accepted genera in Urgineoideae.

FIGURE 30. Species of Iosanthus Mart.-Azorín et al. displayed in horizontal rows of images. 1. Iosanthus amboensis (Baker) Mart.- Azorín et al. (top 3 rows of images) (Photographs by A. Eichhoff); 2. Iosanthus macrostigma Mart.-Azorín et al.

FIGURE 31. Iosanthus macrostigma Mart.-Azorín et al. from Klein Windhoek, Namibia (Type locality). a. Portion of bulb and inflorescence; b. Inflorescence; c. Flower in frontal view; d. Dissected tepals with stamens; e. Tepals with adnate stamens; f. Gynoecia; g. Dissected flower in lateral view; h. Developing capsules; j. Capsules and seeds; k. Seed; m. Leaves. Scales 5 mm.

FIGURE 32. Iosanthus toxicarius (C.Archer & R.H.Archer) Mart.-Azorín et al.