Luino I., M.W. Callmander, O. Poncy, S. Da-Giau & L. Gautier (2016). A new Pararistolochia Hutch. & Dalziel (Aristolochiaceae) from the Beanka tsingy (western Madagascar). Candollea 71 : 135–141. In English, English and French abstracts. DOI : http ://dx.doi.org/10.15553/c2016v711a16
Pararistolochia Hutc. & Dalziel (Aristolochiaceae) is a genus that comprised about 35 species known until present from continental Africa and Australasia. Two recent inventories carried in the limestone massif of Beanka in western Madagascar have led to the detection of a new species that we describe here as Pararistolochia enricoi Luino, L. Gaut. & Callm. This impressive liana is until today the only malagasy representative of the genus. The deciduous habit, together with the two-lobed perianth and the presence of trichomes covering most parts of the plant are exclusive characters that clearly distinguish Pararistolochia enricoi within the genus. The new species is provided with a preliminary risk assessment of its conservation status based on the IUCN Red List Categories and Criteria.
Introduction
As currently circumbscribed, Aristolochiaceae (including Hydnoraceae) is a small family of ca. 500 species in 7–9 genera (Stevens, 2015). The tribe Aristolochioideae is by far the most diverse with ca. 400 species found mainly in the tropics of both old and new world ; but considerably less diverse in Africa and Madagascar, with as few as 20 accepted species (Poncy, 1978; De Groot et al., 2006).
Until the publication of the first volume of the Flora of West Tropical Africa (Hutchinson & Dalziel, 1927) all tropical African Aristolochiaceae species were included in the large pantropical genus Aristolochia L. Pararistolochia Hutch. & Dalziel was described to accommodate 12 African species, based on their elongated indehiscent lignified fruit and their actinomorphic 3-lobed perianth.
Further publications did not all recognize the generic status of the new genus. Starting with Schmidt (1935), the taxonomic level of the separation between Aristolochia and Pararistolochia (generic or infra-generic) has remained an open question.
The African species of Pararistolochia have been revised by Poncy (1978), who defended the separation of the two genera by a thorough analysis of vegetative, floral (including pollen) and fruiting characters. Verdcourt (1986), in Flora of Tropical East Africa, maintained the two genera separate, whereas Jongkind (1990), while describing a new species from Gabon with several characters of Pararistolochia decided to describe it in Aristolochia, arguing that : “At present, the delimitation of Aristolochia s.s. versus Pararistolochia dose not justify the existence of two separate genera.”
Huber (1985) studied the seed anatomy and provided further support to the “separate-genera” position. He also suggested based upon earlier results (Hou, 1983, 1984) that the genus could possibly extend to Australasia. In preparing a revision of the family for Australia and New Guinea, Parsons (1996a) defended the separation of the two genera, transferring 11 species of Aristolochia to Pararistolochia and further describing 12 new species in the genus.
Leal et al. (2011) recently revised the family for the flore du Gabon and chose to treat the two genera as separate, publishing the combination of the species described by Jongkind (1990) in Pararistolochia. Buchwalder (2014) preferred to consider Pararistolochia as a subgenus within Aristolochia, subsequently making the necessary combinations in Aristolochia and listing 35 accepted species in the subgenus Pararistolochia.
In the last 15 years, three different phylogenetic analyses of Aristolochiaceae were carried out at family or subfamily level. All three have confirmed the monophyly of the Pararistolochia clade. In the first one, based on morphological characters of the subfamily Aristolochioideae, González & Stevenson (2002) demonstrate that Aristolochia in its broad sense is paraphyletic, and that it includes a monophyletic Pararistolochia.They propose a revised classification confirming the generic rank for Pararistolochia. The two other studies concern the family Aristolochiaceae as a whole and involve molecular techniques. Neinhuis et al. (2005) confirmed the position of the family within Piperales as well as its subdivision into two subfamilies Asaroideae and Aristolochioideae. Within the latter, results are mostly in congruence with earlier morphological studies (Huber, 1985 ; González & Stevenson, 2002), especially regarding the monophyly of Pararistolochia. Ohi-Toma et al. (2006) increased significantly the numbers of species in a molecular phylogeny of Aristolochia s.l. and came to the conclusion that it could be divided in two major lineages : the “Isotrematinae clade” (with the genera Isotrema Raf. and Endodeca Raf.) and the “Aristolochiinae clade”, which is further subdivided into Aristolochia s.s. and Pararistolochia.
These results make clear that Pararistolochia is a valid taxonomic entity. Its rank in the classification will depend on the rearrangement of the taxa within the family, based on phylogenetic patterns at the family level. Pending this taxonomic and nomenclatural statement, we have chosen to describe the new species from Madagascar in Pararistolochia, because in our opinion, the morphological and molecular characters that separate the two lineages are clearly sufficient to consider them as separate genera.
During a floristic inventory of the Beanka forest, in western Madagascar (Gautier et al., 2013) (Fig. 1) that has already led to the discovery of several new species in various families, e.g. Anacardiaceae (Randrianasolo & Lowry, 2015), Loranthaceae (Callmander et al., 2013) and Pandanaceae (Callmander et al., 2014), we collected a specimen of Aristolochiaceae that we could not match to any described species. The only species of the family so far accepted from Madagascar is Aristolochia albida Duch., recorded also widely in continental Africa (Senegal to Southern Sudan, down to Angola and Mozambique), the Comoros and the Mascarenes (De Groot et al., 2006).This new species is described below in the genus Pararistolochia and represents the first species of the genus in Madagascar. We provide a discussion of its morphological affinities together with colour pictures and line drawings. A preliminary risk assessment following IUCN Red List Categories and Criteria is also provided (IUCN, 2012).
Pararistolochia enricoi Luino, L. Gaut. & Callm., spec. nova (Fig. 2, 3).
Typus : Madagascar. Prov. Mahajanga : Melaky Reg., Beanka, partie S, 18°07′22″S 44°33′31″E, 300 m, 30.XI.2012, fl., Gautier, Ranirison, Hanitrarivo & Luino 5886 (holo- : G [G00341650]!; iso- : K!,MO!, P [P00853247]!,TEF!).
Species nova quae a congeneris trichomatibus plantae partes omnes praeter caulem lignosum obtegentibus, perianthio bilobo atque foliis papyraceis deciduis perclare distat.
Climbing and ground sprawling, deciduous vine or liana. Stems to 15–25 m high, cross section flattened in the central part resulting in an 8-shape, up to 1.5 cm in width; bark of the oldest stems brown-yellow, corky, verrucate. Leaves margins entire ; lamina, 4-8 × 3-6 cm, green above, paler below, papery, sparsely pubescent on both surfaces (white indumentum of simple, multicellular trichomes), shape variable, ovate to hastate ; base rounded to cordate, auricles well rounded when present, sinus 0.1–1 cm deep or absent; apex rounded to slightly acuminate, sometimes apiculate ; primary veins 3–5, prominent beneath, slightly elevated above, pubescent ventrally and dorsally ; secondary veins reticulate ; petiole slender, 0.9–2.5 cm long, 0.8–1.1 mm wide; young shoots attenuate, densely covered with a golden indumentum. Inflorescences arising from the corky stem, sometimes at ground level, solitary or fasciculate by 2–3, consisting of a 5–7 flowered raceme; rachis up to 20 cm long, with irregularly spaced internodes between 1 and 10 cm long; bracts 1–4 mm long, densely pubescent; pedicels 15–30 mm long. Flowers buds densely covered by a golden indumentum, with two bulgings corresponding to the young utricule and perianth lobes. Mature flowers up to 48 mm long overall, all the parts covered by a white indumentum ; perianth tube S-curved, 15(-18) mm long, funnel-shaped, enlarging throughout and constricted below the throat, flaring from 4 mm in diam. above the utricule to up to 10 mm in diam. in its widest part ; throat bright sulphur-yellow, pubescent with white 1.5 mm long setae ; lobes 2, triangular to well-rounded, sometimes slightly apiculate, purple, 10 mm long, margins outwardly rolled, dark purple ; utricle obovoid, externally white, punctuated with small red spots, purple veined, 11 mm long by 6 mm wide ; gynostemium 2.7 mm long by 1.6 mm wide, anthers 6, 1.3 mm long, yellow, each consisting of 4 pollen sacs, stigmatic lobes 6, 1.4 mm long, green, with a short, subconical, sharp apical appendage ; ovary cylindrical, 6-ribbed, densely covered by a white indument, 10 to 14 mm long. Fruits pendulous, cucumber-like, curved-cylindrical, indehiscent, woody, prominently 6-ribbed, to 5.5 cm long by 2.8 cm wide, yellow and pubescent when immature, brown and sparsely pubescent when mature. Seeds stacked in 6 simple rows, heart-shaped convex and rough above, concave and smooth below, 4 mm long by 4 mm wide.
Etymology. — The species is named in honour of the first author's brother Enrico Luino who died in 2003 at the age of 21. Enrico triggered in him the passion for tropical botany.
Distribution and ecology. — Pararistolochia enricoi is only known from the eroded limestone formations (“Tsingy” in Malagasy) of Beanka in western Madagascar (Fig. 1). Its ecology seems to be strongly related to the climax deciduous forest type, where it grows in shaded conditions. According to the collection period, anthesis takes place in November and fruits ripen between December and January. The plants presenting only young leaves at the moment of the flowering collection, we conclude that, given the papery texture and the thin lamina of the fruiting sample, the species is deciduous and that leaves are absent during the dry season, generally from May to October.
The plant-insect interactions of Pararistolochia enricoi are still unknown. In western and southern Madagascar the monospecific butterfly genus Pharmacophagus antenor (Drury, 1773) (the only representative of the tribe Troidini in Madagascar) is known to be monophagous on Aristolochia albida (Parsons, 1996b). As documented by Parsons (1996a), the larvae of the troidine papilionid butterflies of the Australasian genus Ornithoptera feed primarily on Pararistolochia in the Australasian region. Considering the overlapping distributions of P. enricoi and Pharmacophagus antenor together with the known feeding habits of the latter, one could hypothesize that P. antenor larvae also feed on Pararistolochia enricoi.
Conservation status. — Pararistolochia enricoi is known only from two locations within a proposed protected area with temporary protection (Beanka).The new species is restricted to karstic limestone, an area with no evident human caused damage or alteration. Even if it currently has a very restricted range, the new species is probably under little if any threat, and is here assigned a preliminary status of Least Concern [LC].
Notes. — Pararistolochia enricoi is the second species within the family Aristolochiaceae in Madagascar. It can only be compared with Aristolochia albida Duch. but several characters clearly discriminate the new species. Pararistolochia enricoi differs from Aristolochia albida, also present in Beanka, by its habit (a woody liana up to 16 m long vs. a smaller, non-woody vine), the 8-shaped cross-section of the stem (vs. circular cross-section), the presence of indumentum on most parts (vs. glabrous), the S-shaped perianth tube with two subequal lobes (vs. straight tube with a single lobe) and the indehiscent cucumber-like fruit (vs. dehiscent basket-like fruit) (Fig. 2, 3). Furthermore, Pararistolochia enricoi is the only deciduous species of the genus and the first to be recognized in Madagascar. We have discussed in the introduction the reason why we consider Pararistolochia as a distinct genus from Aristolochia. However, it should be noted that even among Pararistolochia, our species has the very striking feature of a bilobed corolla (instead of a tri-lobed corolla in all other species in the genus). Hopefully molecular investigations will further confirm its generic affinities.
Paratypi. — Madagascar. Prov. Mahajanga : Beanka, partie centrale, 17°56′53″S 44°28′57″E, 190 m, 11.II.2012, fr., Rakotozafy, Bolliger & Hanitrarivo 40 (G,TEF) ; ibid. loc., 18°01′46″S 44°30′18″E, 260 m,4.XI.2015, fl., Luino 116 (G, P, MO, K,TEF) ; ibid. loc., 18°01′46″S 44°30′18″E, 260 m, 15.XI.2015, fl., Luino 247 (G, P, MO, K, TEF); ibid. loc., 2.XII.2015,y. fr., Luino 248 (G, P, MO, K,TEF).
Fig. 1.
Detailed map of western Madagascar showing the distribution of Pararistolochia enricoi Luino, L. Gaut. & Callm. (stars) in Beanka, plotted on a map of forest cover in 2000 (grey) following Harper et al. (2007).
Acknowledgements
The authors thank the staff of the following institutions for logistical and collaborative support : Département de Biologie et Ecologie Végétales de l'Université de Genève, Missouri Botanical Garden in Antananarivo, Vahatra association and Famelona association in Antananarivo and Conservatoire et Jardin botaniques de la Ville de Genève. We are grateful to Brice Funk Lee Rakotozafy for the paratype specimen collection and Gabriela Loza for her nice contribution to the line drawings. We thank Adélaïde Stork, Jean-Pierre Lebrun and Pete Phillipson for support and interest in our work. Finally we thank George Schatz for his review that improved an earlier version of the manuscript and for advices on the risk of extinction assessment. Financial support was provided to IL & LG by grants from the Vontobel Foundation, and to IL by a scholarship of the Ernst and Lucie Schmidheiny Foundation and by the Young Explorer Grant of the National Geographic Society.
