The rediscovery of Euphorbia caput-aureum Denis (Euphorbiaceae) Sébastien Houyelle Through careful research and with the help of locals, the author describes the rediscovery of a species of Euphorbia from northern Madagascar, last collected in 1910. All photos by the author. Introduction Euphorbia caput-aureum was discovered by H Perrier de La Bâthie in November 1909 and collected again in March 1910, in north-western Madagascar on ‘Mount Mahabenofo’. Two samples were deposited in the herbarium of the National Museum of Natural History in Paris (Perrier 10647 and Perrier 10695). The species was finally described in 1921 by Marcel Denis in Les euphorbiées des îles Autrales d’Afrique (Denis, 1921). In volume II of Rauh’s Succulent and xerophytic plants of Madagascar (Rauh, 1998) he states that the species was never re-collected. In the IUCN Red List (Haevermans, 2004), its status as a species was questioned, “The species is very close to other similar species described by W Rauh (such as Euphorbia iharanae, E. aureoviridiflora, etc), all very localised. Unfortunately the only collection of E. caput-aureum is located on ‘Mount Mahabenofo’, this locality does not exist anymore and is absent from all the known gazetteers. Further fieldwork and taxonomic work is required to ascertain the status of the species and its relationships (synonymy) with closely related taxa.” Exploration Before leaving for Madagascar and the unknown, it was necessary to consult the above mentioned herbarium in Paris in order to study the information on the herbarium sheets. We also had to obtain some detailed maps of the country and to cross-reference all available information. After half a day of research we eventually located a zone which seemed to correspond with what we were looking for. Fig. 1 View of Mount Mahabenofo CactusWorld 2015 Vol. 33 (2) 125 Fig. 2 Euphorbia caput-aureum in flower during the winter So it was that during our latest expedition to Madagascar, Christophe Quenel and I decided to follow in the footsteps of Perrier de la Bâthie, in search of Euphorbia caput-aureum. As amateur botanists, collectors and passionate about Madagascan Euphorbia, we had already been intrigued by this species for quite a few years. In the capital, Tananarive, on 23 July 2014 the decision was taken to make the trip the following day. We thought that it would be essential to take with us an example of a species which was similar to E. caput-aureum, and decided on E. iharanae. From experience, we knew that having an actual plant with us for comparison and to show locals, would be much more useful than any photographs. Fig. 3 An old specimen of E. caput-aureum by the forest edge 126 CactusWorld 2015 Vol. 33 (2) We travelled to the north of the island and two days later we arrived in a village near the mountainous zone which we had previously identified on the map, and went to the first house looking for information. First of all, we asked a native Malagasy about the name of the big mountain which was behind us, and he answered, “Mahabenofo”. Then we showed him the plant that we had with us (E. iharanae) and he told us that there were many of them in the surrounding mountains. Finally we asked him what colour the flowers were and he responded, “yellow”. For us, all the responses matched our expectation that this was probably E. caput-aureum. Unfortunately, we did not have any more time that day to look for these plants in situ, because we still had a long journey ahead of us and other plants to search for. Before heading back on the road, we asked him if he could collect a specimen for us and told him that we would return three days later. Fig. 4 The stem of E. caput-aureum Upon our return, he showed us a superb plant with the added bonus that it was in flower, which matched the description of Denis’s Euphorbia caput-aureum. We then asked him to take us to the place where he had found the plant. Expecting to be taken to Mount Mahabenofo itself, contrary to our expectation, he brought us to a rocky ridge line, in front of the mountain. We spent the whole morning exploring the site and noticed that the species grows in small groups, here and there, but always on the edge of the forest along the rocky crest. Description Fig. 5 Close-up of the inflorescence of E. caput-aureum Stem 5-angled, slightly spirally twisted, branched or unbranched. Leaves obovatespatulate, 3–12cm long, 2–3.5cm wide, apex mucronate, base narrowed; stipular spines solitary, 8–12mm long, sometimes with smaller prickles at base. Inflorescence subterminal, densely capitate, with 10–20 subsessile cyathia; cyathophylls erect, goldenyellow, pubescent, completely hiding the involucre. Cyathia golden-yellow, pubescent; glands elliptic, yellow; male flowers pubescent below anthers. Ovary glabrous, shortly pedicellate; style half joined. Capsule shortly pubescent. Conservation This species grows in small pockets of humus on loose bare rocks, along a rocky crest at an altitude of 200m, near Mount Mahabenofo, in association with Aloe sp, Cyphostemma sp, Kalanchoe sp, Commiphora sp, Adenia sp and Euphorbia sp. E. caput-aureum is scarce in habitat. We estimated the population to be around 400 individuals on this site and our guide told us that there would be more on Mount Mahabenofo itself. Given that there are approximately 400 plants on the ridge line and 1,000 on the other site, this would give around 1,400 individuals in total on both sites. Consequently E. caput-aureum is a vulnerable species and probably in danger in the forthcoming years. LITERATURE CITED: Denis, M (1921) Euphorb. Iles Austr. Afr. p73. Haevermans, T (2004) Euphorbia caput-aureum. The IUCN Red List of Threatened Species. Rauh, W (1998) Succulent and xerophytic plants of Madagascar. Strawberry Press, Mill Valley, USA. Vol 2: 149. Sébastien Houyelle 76 Chemin Adam de Villiers, 97430 Tampon, France Email: [email protected] Christophe Quenel: http://www.madabotanik.com Fig. 6 A small seedling in situ Layout by Jim Mercer CactusWorld 2015 Vol. 33 (2) 127