Thermogenesis in Syngonium (Araceae) Mathieu Chouteau, Denis Barabe ´ , and Marc Gibernau Abstract: Floral cycles and spadix temperatures were recorded for two species of Syngonium: Syngonium schottianum Wendl. ex Schott (section Cordatum) and Syngonium angustatum Schott (section Syngonium). Both species exhibited a 3- day flowering cycle, beginning with stigma receptivity and opening of the spathe the first day, the female phase continues over the second day, and the male phase continues over the third day. These species displayed two distinct patterns of heat production during flowering. In S. schottianum, the spadix warmed up twice during the beginning of the second and third nights, but in S. angustatum, the spadix warmed up twice the second day, once the second night, and once the third day. These different thermogenic cycles are discussed in regard to other genera that are phylogenetically close or sharing similar flowering and thermogenic cycles. Key words: Syngonium, Araceae, flowering cycle, thermogenesis. Re ´sume ´: Les auteurs ont etudie ´ les cycles floraux et les tempe ´ratures des inflorescences chez deux espe `ces de Syngo- nium : Syngonium schottianum Wendl. ex Schott (section Cordatum) et Syngonium angustatum Schott (section Syngo- nium). Les deux espe `ces posse `dent un cycle floral de trois jours, de ´butant avec la re ´ceptivite ´ des stigmates et l’ouverture de la spathe le premier jour, la phase femelle continue le deuxie `me jour, suiviede la phase ma ˆle le troisie `me jour. Ces es- pe `ces exhibent deux types distincts de courbes de tempe ´rature des spadices. Chez le S. schottianum, le spadice produit deux pics distincts de chaleur au de ´but des seconde et troisie `me nuits, tandis que chez le S. angustatum, le spadice produit des pics de chaleur deux fois au cours de la premie `re journe ´e, une fois la deuxie `me nuit, et une fois la troisie `me journe ´e. Les auteurs discutent ces diffe ´rences de cycles thermoge `niques, en relation avec d’autres genres phyloge ´ne ´tiquement voi- sins ou qui ont des cycles similaires de floraison et de thermogene `se. Mots-cle ´s : Syngonium, Araceae, cycle floral, thermogene `se. [Traduit par la Re ´daction] Introduction Thermogenesis in reproductive organs is common in the Araceae but also exists in several other plant families: An- nonaceae, Arecaceae, Magnoliaceae, Nymphaeaceae, and Zamiaceae. Heat production by floral structures is generally associated with emission of fragrances, arrival of pollinators, and liberation of pollen (Tang 1987; Gottsberger 1990; Yafuso 1993; Azuma et al. 1999; Seymour 1999; Thien et al. 2000; Lamprecht et al. 2002). Although numerous studies have focused on the production of heat by inflorescences of Araceae, few of them document the complete thermogenic cycle (Nagy et al. 1972; Seymour et al. 1983; Barabe ´ and Gibernau 2000; Gibernau et al. 2000, 2003; Gibernau and Barabe ´ 2000; Ivancic et al. 2004, 2005; Maı ´a and Schlindwein 2006). Thermogenesis and the flowering cycle have not been studied in the neotropical genus Syngonium, which consists of over 32 species (for unpublished observations see Beath 1998). The protogynous inflorescences of the genus Syngo- nium bear small flowers enclosed in the spathe (Fig. 1). The pistillate flowers occupy the lower portion of the spadix, whereas the male flowers are located on the upper portion. In the median portion of the spadix, there is a zone consist- ing of sterile male flowers (Fig. 1). The genus Syngonium belongs to the Caladieae tribe, which contains seven genera, including Xanthosoma and Caladium (Mayo et al. 1997; Barabe ´ et al. 2004). Given that floral morphology, flowering cycle, thermogenic pattern, and pollinators (beetle) of Cala- dium (Maı ´a and Schlindwein 2006) and Xanthosoma (Garcı ´a-Robledo et al. 2004) are similar to those of Philo- dendron, which have been studied in detail (Gibernau et al. 1999, 2000; Gibernau and Barabe ´ 2000, 2002; Barabe ´ et al. 2002), one would expect to find the same pollination mech- anism in Syngonium. Our study measured the temperature in the different zones of the spadix for two Syngonium species belonging to two different sections (i) Syngonium schottianum Wendl. ex Schott (section Cordatum) and (ii) Syngonium angustatum Schott (section Syngonium). The temperature of the spadix was recorded during the entire flowering cycle, and at the same time the flowering behaviour (movement of the spathe, odour production, pollen release) was recorded on plants grown under greenhouse conditions. The specific goals of this study are (i) to characterize the pattern of heat production in two different sections of the genus Syngonium,(ii) to compare the thermogenic cycle of Syngonium with phylogenetically related genera, and (iii) to analyze the thermogenic pattern of Syngonium in relation to the putative mechanism of pollination in this genus. Received 11 November 2006. Published on the NRC Research Press Web site at http://canjbot.nrc.ca on 3 May 2007. M. Chouteau and D. Barabe ´. 1 Institut de recherche en biologie ve ´ge ´tale, Universite ´ de Montre ´al, Jardin Botanique de Montre ´al, 4101 Rue Sherbrooke Est, Montre ´al, QC H1X 2B2, Canada. M. Gibernau. Universite ´ Paul Sabatier, Laboratoire d’e ´volution et diversite ´ biologique (UMR 5174), Ba ˆtiment 4R3-B2, 31062 Toulouse CEDEX 9, France. 1 Corresponding author (e-mail: denis.barabe@umontreal.ca). 184 Can. J. Bot. 85: 184–190 (2007) doi:10.1139/B07-004 # 2007 NRC Canada