Litsea glutinosa (Lour.) C. B. Rob., l’avocat marron, est un arbre dioïque d’Australasie qui a été introduit à Mayotte et multiplié à l’époque de la canne à sucre (1841-1880). Disséminée efficacement par les lémuriens (Eulemur fulvus) et par de nombreux oiseaux, cette Lauraceae s’est étendue sur toute la zone humide et est présente dans les dernières forêts «naturelles » fragmentées de l’île. Cet arbre de 10 à 15 mètres de hauteur se concentre actuellement dans les deux-tiers nord plus arrosés (pluviosité > 1 500 mm/ an) de Mayotte. Ce travail analyse la dynamique entre 1996 et 2002 des populations de Litsea glutinosa établies dans les reliquats de forêt mésophile et ombrophile et la part de la multiplication végétative dans certaines populations. L. glutinosa prolifère dans les réserves forestières et particulièrement en forêt semi-sèche en fonction de la structure forestière plus ou moins ouverte. Par son tempérament héliophile, cette espèce nécessite une perturbation pour croître et se fixer en forêt. Sa persistance et son caractère envahissant sont dus en partie à sa possibilité de multiplication végétative à l’origine de plus de la moitié des fûts, principalement par drageonnage. Cette espèce constitue un risque d’appauvrissement spécifique dans les zones «naturelles» sans pour autant être considérée par les mahorais comme une peste en raison de sa fréquente utilisation en particulier comme plante fourragère.

The new species Pandanus papateaensis Butaud, F. Jacq & Callm. (Pandanaceae) is described from the uplifted atoll of Makatea located in the Tuamotu Archipelago of French Polynesia. The new species can be distinguished from other Polynesian species by its completely fused drupes with usually two seminal chambers and by its reddish-brown to darkpurple pileus, which totals more than one third of the total length of the drupe. Pandanus papateaensis is known from a few subpopulations located on the edge of the central plateau and it occurs in sympatry with Pandanus tectorius Parkinson. The species is known by less than 80 individuals and its sustainability is threatened by a phosphate mining project, which could have a significant impact on two of the three subpopulations. Based on the latter evidence, the new species is assigned a preliminary "Endangered" [EN] status following IUCN Red list Categories and Criteria. A regulatory protection status is thus recommended for this new species, as well as for the exceptional natural vegetation formations of this atoll, which is threatened by 50 years of intense phosphate mining without any current restoration programs to compensate for the damage caused. Résumé

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Mortality rate and extinction causes of Apetahia raiateensis (Campanulaceae), an endemic plant to the island of Raiatea (French Polynesia). — Identifying the causes of extinction and their intensity is a prerequisite to define the status of species conservation and to set up efficient and effective conservation plans. Apetahia raiateensis H. Baillon (Campanulaceae), an endemic shrub on three trachytic plateaus of the island of Raiatea (Society Islands), is a legendary plant in Polynesian culture and a legally protected species in French Polynesia. Systematic inventories were conducted on the plateaus Te mehani ‘ ute’ute (94 ha), Te mehani rahi (202 ha) and Te vaihue (12 ha) to assess populations (882 plants in 2009), to map the species, and to compare with previous inventories performed in 1995. 81 accessible plants and 820 of their stems were monitored on Te mehani rahi between 2009 and 2011, in order to quantify and understand the reasons of the species rapid extinction. The inventories revealed a rate of disappearance to be respectively of 74 % on Te mehani ‘ ute’ute (1995-2006) and of 76 % on Te mehani rahi (1995-2009). The plants are currently found in subpopulations restricted on the borders of the plateaus and on cliffs. After 18 months of follow-up, 41 out of 57 reproductive plants (72 %) and 219 stems were attacked by rats (Rattus spp.) and 9 reproductive plants and 133 stems were found dead. In addition, 31 % of these reproductive plants had 29 stems broken by people. Among the wilted stems with unknown causes, half (55 stems on 15 plants) might be related to the cyclone that hit Raiatea in 2010. The species habitat is also threatened by feral pigs and by the invasion of twelve naturalized alien plants. Our results support the classification of Apetahia raiateensis in the «critically endangered» category (CR) of IUCN. Rat control trials using baits around plants are currently conducted on Te mehani rahi, together with in situ propagation from seeds, for the recovery of this species of scientific and cultural heritage values.