Dioscorea galiiflora R. Knuth. Notizblatt des Botanischen Gartens, 1921

Fraga, Fernanda Ribeiro De Mello, Couto, Ricardo Sousa & Braga, João Marcelo Alvarenga, 2019, The threatened Dioscorea galiiflora and the identification of Dioscorea triangularis (Dioscoreaceae): Solving a secular imbroglio, Phytotaxa 391 (2), pp. 93-100 : 94-97

Dioscorea galiiflora R. Knuth. Notizblatt des Botanischen Gartens und Museums zu Berlin-Dahlem 7: 538. 1921.

Type:― BRAZIL, Mato Grosso: Tapirapoan, March 1909, fl. ♂, F.C. Hoehne 1625 (Holotype: B 100243969!).

Dioscorea triangularis (Griseb.) R. Knuth In : Engler, Der Pflanzenreich 4(43): 57. 1924, nom. illeg. (non Sessé & Mocino 1894), auct. non.

Twining vine, dioecious, glabrous. Stems climbing, left-twining, herbaceous, terete, striated, unarmed. Leaves alternate, ovate to triangular; blade monomorphic, entire to slightly irregular, 7.9–9.5 × 7.0– 8.4 cm, veins 7(–9), primary venation prominent below; base cordate to truncate, with two basal lobes, with narrow basal sinus; apex acuminate, membranaceous to papyraceous, dark green above and bright green below, with glands in the center of deep sinus; petiole ca. 3 cm long, twisted, striated, canaliculated, terete; lateral nodal organs and axillary tubercle not seen. Staminate inflorescence 7.9–12.1 cm long, pendent, heterothetic compound inflorescence with racemes on principal axis and cincinnus on secondary axis, with 2–3 flowers per node, ca. 0.2 cm long apart. Staminate flowers 1–3 mm long, with one pair of bracteoles ca. 1 mm long, diminutive, deltoid, membranaceous; filiform pedicels 2–4 mm long; tepals 6, outer tepals ca. 2 mm long, obovate-acuminate; inner tepals ca. 2 mm long. oblong, perianth rotated, 3-nervi; stamens 6, filaments minute to inconspicuous; anthers enclosed, centrally disposed, slightly raised on central disc; pistillode inconspicuous or absent. Pistillate inflorescence 19–20 cm long, simple, spicate, pendent, 1 per axil. Pistillate flower 1–3 mm long, sessile, 1 per node, oblong to elongated, with a pair of acute membranaceous bracteoles; perianth rotate, inner and outer tepals ca. 2 mm long, oblong to acute, membranaceous, glabrous; 3-carpel gynaeceum, style 3, free in their biggest extension, without staminodium. Immature capsules 0.7–1.2 × 0.42–0.53 cm, sessile, oblong to elongated, with persistent perianth in the apex. Seeds not seen.

Preliminary Conservation Status:—According to the available data, conservation assessment performed here considered geographic range (namely, B criteria by IUCN 2012). The species has been recorded in two states in central plateau of Brazil. The short distance between the few extant specimens diminishes the Extent of Occurrence (EOO, Criteria B1) to 145,473.208 km ², lower than 5000 km ² (B1.2). The Area of Occupation (AOO, Criteria B2) has only 20 km ², lower than 500 km ² (B2.2). Furthermore, the species is known from only five localities, which are currently subject to agriculture and other changes of land use. None of the sites is within protected areas. Therefore, both conditions of number of localities and continuing declining are met, leading the analyses to the Endangered (EN) category, following the IUCN Red List categories and criteria ( IUCN 2012). The distribution of Dioscorea galiiflora , D. piperifolia complex and D. moyobambensis is represented in Fig. 1 .

Material Examined:— BRAZIL. Goiás: Bucaina , s.d., fl. ♂, Pohl 1245 ( BR) ; Vila Boa , s.d., fl. ♂, Pohl 2511 ( B, BR, F) ; Mato Grosso: Campina , S. L. de Cáceres, January 1909, fl. ♂, Hoehne 1042 ( R) ; Coxipó Mirim , 2 September 1894, fl. ♀, fr., Malme s.n. ( S 1547424 ) ; Coxipó Mirim , 2 September 1894, fl. ♂ ♀, fr., Malme s.n. ( S 1547414 ) ; Coxipó da Ponte , March 1911, fl. ♂, Hoehne 4633 ( R) ; s.loc., s.d., fl. ♂, Pohl s.n. ( BR 659766 ) .

Taxonomic Notes: —Comparison of the descriptions of D. triangularis and D. galiiflora and the plant material studied made it clear that the inflorescence arrangement of both have been misinterpreted as spikes and racemes, respectively. In fact, older descriptions of Dioscorea commonly prioritize vegetative structures over reproductive ones. This is seen in D. laxiflora Martius ex Grisebach (1842: 32) , which consists of seven varieties distinguished only by leaf shape and size. Another example is D. piperifolia and its varieties. When Grisebach (1842) described D. piperifolia he thoroughly described the leaves of each variety. Descriptions for the inflorescences instead were only provided for D. piperifolia . These were described as simple racemes, rarely with fascicles.

The inflorescences were inaccurately described for all the species involved in this imbroglio. Heterothetic compound inflorescence with racemes on principal axis and cincinnus on secondary axis are considered as racemes by Knuth (1921) and later as simple spikes with 2–3 flowers per node (see Knuth 1924). Proper understanding of the inflorescences also relies on their stage of development, which explains Knuth’s misinterpretation. Since inflorescences show indefinite growth, it is difficult to distinguish simple racemes, with one flower per node, from immature cincinnus when buds still do not show their direction of growth. However, the inflorescence structure is a much more stable trait in Dioscorea than the shape and size of leaves, or other vegetative traits. In fact, no differences are observed between the inflorescences of the D. piperifolia complex, which has only simple inflorescences in raceme, or between all studied specimens of D. galiiflora and D. moyobambensis , which have only heterothetic compound inflorescence with racemes on principal axis and cincinnus on secondary axis.

Besides inflorescence structure, flower morphology is also helpful to circumscribe species in Dioscorea . In general, the number of nerves on tepals is a good diagnostic character, since most species have a single nerve. In the D. piperifolia complex the tepals exhibit different shapes, but they have always three nerves. The same is seen in D. galiiflora , but not in D. moyobambensis , which have tepals with only one nerve. The tepals of D. galiiflora are obovate and stamens are sessile, central and not-elevated, while D. moyobambensis has lanceolate tepals and sub-sessile (elevated) stamens. Meanwhile, central, sessile, not-elevated stamens are seen in D. piperifolia complex. Therefore, inflorescence and flower morphology allow us to confidently circumscribe the species here analysed. Diagnostic characters for each species are summarized in Table 1. Differences in tepal venation and inflorescence architectures are illustrated in Fig.2 and Fig. 3 ; respectively.

Nomenclatural Notes:― Willdenow (1806) published Dioscorea piperifolia based on the annotations of Humboldt & Bonpland and their collections: “Habitat in India occidentali et America meridionali”, a gathering of Humboldt & Bonpland 2219 ( B!, P!, W!) from Quito, Ecuador. Grisebach (1842) proposed two new varieties for this species: D. piperifolia var. glandulosa Klotzsch ex Grisebach and D. piperifolia var. triangularis Grisebach , naming the Willdenow (1806) type variety as Dioscorea piperifolia var. “ legitima”. Grisebach (1842) listed several specimens as type of D. piperifolia var. glandulosa , but for D. piperifolia var. triangularis the author only indicated “in prov. Goyaz, prope Villa Boa: Pohl ♂ ” ( M 213505!). Lectotypification of D. piperifolia var. glandulosa is currently work in progress.

Dioscorea moyobambensis is another species in the Dioscorea sect. Centrostemon , very similar to the taxa discussed above. Knuth (1917) published D. moyobambensis , typified it with a gathering from Peru, Weberbauer 4621, and described its inflorescences as fascicles of 2–3 flowers per inflorescence node. Later, he described D. galiiflora ( Knuth 1921) based only on Hoehne 1625 ( B!), a plant gathered at Mato Grosso State (Tapirapoan) in the central plateau of Brazil, on March of 1909. The author described this new species as having 3–6 flowers at each cyme in the main inflorescence, with rotated perianth flowers and six stamens. The holotype, housed at B, exhibit heterothetic compound inflorescence with racemes on principal axis and cincinnus on secondary axis, being the rest of the diagnostic characters listed by Knuth (1921) easily recognizable.

Although the type of D. moyobambensis has compound inflorescences and six stamens, it is possible to distinguish it from the other two species ( D. piperifolia and D. galiiflor a) by its flowers with 1-nerved tepals and elevated stamens. Furthermore, the current geographic range of D. moyobambensis is restricted to Peru, and does not overlap with the distribution range of D. galiiflora (see Fig. 1 ). Three years after describing D. galiiflora, Knuth (1924) made a new combination for D. piperifolia var. triangularis , when elevating the variety to species level, publishing the name D. triangularis (Grisebach) R. Knuth. However , thirty years earlier, Sessé & Mocino (1894: 232) published D. triangularis in Flora Mexicana. The protologue indicates a short description of the type locality, without reference to the collector or herbarium where the specimen was housed. Téllez-Valdés et al. (2010) designated a lectotype ( MA 600264! F neg.43319!) and recognized D. triangularis Sessé & Mocino as a synonym of Dioscorea convolvulacea Schlechtendal & Chamisso (1831: 49) . This species differs from D. piperifolia var. triangularis in several morphological traits such as number of stamens (3 in D. triangularis and 6 in D. piperifolia var. triangularis ). Therefore, the new combination by Knuth (1924) is a latter heterotypic homonym of D. triangularis ( Sessé & Mocino 1894: 232) , making it an illegitimate name ( Turland et al. 2018, Art.11.1). Knuth (1924) also added new gatherings in his description of D. triangularis and explicitly listed two of them as type material, Pohl 1245 ( B!) and Pohl 2511 ( B!). However, the basionym type is not mentioned. Furthermore, all the specimens examined and presented by Knuth (1924) for D. triangularis have compound inflorescences in cincinnus, differing from the simple racemes seen in the D. piperifolia var. triangularis and in the D. piperifolia complex, making D. triangularis a case of auctorum non (misapplied name) ( Turland et al. 2018, Rec. 50D.1).

After studying all the material cited as types, and comparing with collections stored at several herbaria, for each of the species discussed above, we conclude that the varieties of D. piperifolia described by Grisebach (1842) are in fact part of the D. piperifolia complex. Furthermore, we consider D. galiiflora a valid species and distinct from D. moyobambensis . Dioscorea triangularis (Griseb.) Knuth , on the other hand, is an invalid name that refers to a different entity from that referred to in the original description and material listed by the author. Thus, it is an auctorum non, and synonym of D. galiiflora .

Figures

FIGURE 1. Distribution map of the Dioscorea piperifolia complex, D. galiiflora and D. moyobambensis.

FIGURE 2. Floral morphology: A. Scheme of a 1-nerved, lanceolate tepal of D. moyobambensis; B. Scheme of a 3-nerved, obovate tepal of D. galiiflora. C. Scheme of a 3-nerved, oblong tepal of D. piperifolia complex. D. Flower of D. moyobambensis with 1-nerved, lanceolate tepals and sub-sessile stamens (Weberbauer 4621, B). E. Flower of D. galiiflora with 3-nerved, obovate tepals and sessile stamens (Hoehne 1625, B). F. Flower of D. piperifolia complex with 3-nerved, oblong tepals and sessile stamens (Pohl s.n., M213505). Photographs by R.S. Couto.

FIGURE 3. Architecture of Inflorescences: A-B. Scheme of a compound inflorescence with cincinnus in lateral (A) and upper (B) view. C. Scheme of raceme in lateral view. D-E. Cincinnus of D. galiiflora (Hoehne 1625, B) and D. moyobambensis (Weberbauer 4621, B), respectively. F. Raceme of D. piperifolia complex (Pohl s.n., M213505). Photographs by R.S. Couto.