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| (c) Monanthotaxis couvreurii, flower showing basally fused stamens; (d) Monanthotaxis whytei, cauliflorous flower with nine hardly visible staminodes alternating with nine stamens; (e) flowers of Monanthotaxis poggei showing four petals and eight stamen, each in a single whorl; (f,g) Monanthotaxis diclina, female flower with one petal removed showing many carpels, and fruits showing multiple seeds per monocarp; (h) Monanthotaxis paniculata fruits with single seed per monocarp.
in Hoekstra, Wieringa, Smets & Chatrou, 2018.
— Photographs: (c,f–h) Thomas L.P. Couvreur; (d) Lubbert Y.T. Westra; (e) Bart T. Wursten.
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Abstract
Simplification by reduction has occurred many times independently in the floral evolution of angiosperms. These reductions have often been attributed to changes in reproductive biology. In the angiosperm plant family Annonaceae, most species have flowers with six petals, and many stamens and carpels. In the genus Monanthotaxis several deviations from this pattern have been observed, including flowers that contain three petals and three stamens only. New DNA sequences were generated for 42 specimens of Monanthotaxis. Five chloroplast markers and two nuclear markers for 72 out of 94 species of Monanthotaxis were used to reconstruct a phylogeny of the genus, which revealed several well-supported, morphologically distinct clades. The evolution of four quantitative and two qualitative floral characters was mapped onto this phylogeny, demonstrating a reduction in flower size and number of flower parts in Monanthotaxis. A large variation in stamen forms and numbers, strong correlations between petal size, stamen and carpel number, combined with a non-gradual mode of evolution and the sympatric co-occurrence of Monanthotaxis species from different clades suggest that the high diversity in the African rainforest of this genus is caused by switches in pollination systems.
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| Figure 1 Flower morphology of outgroups (a) and flowers and fruits of Monanthotaxis (b–h). (a) Uvaria scabrida, flower showing many stamens and carpels; (b) Monanthotaxis bidaultii male flower showing three petals and three stamen; (c) Monanthotaxis couvreurii, flower showing basally fused stamens; (d) Monanthotaxis whytei, cauliflorous flower with nine hardly visible staminodes alternating with nine stamens; (e) flowers of Monanthotaxis poggei showing four petals and eight stamen, each in a single whorl; (f,g) Monanthotaxis diclina, female flower with one petal removed showing many carpels, and fruits showing multiple seeds per monocarp; (h) Monanthotaxis paniculata fruits with single seed per monocarp.
— Photographs: (a) Paul H. Hoekstra, (b) Ehoarn Bidault; (c,f–h) Thomas L.P. Couvreur; (d) Lubbert Y.T. Westra; (e) Bart T. Wursten.
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Paul H. Hoekstra, Jan J. Wieringa, Erik Smets and Lars W. Chatrou. 2018. Floral Evolution by Simplification in Monanthotaxis (Annonaceae) and Hypotheses for Pollination System Shifts. Scientific Reports. 8(12066). DOI: 10.1038/s41598-018-30607-2 1
'Small is Beautiful': floral evolution in Monanthotaxis, a tiny-flowered yet species-rich African genus of #Annonaceae. Just out in Scientific Reports, https://goo.gl/dc6y7a . @PirieMike @tlpcouvreur @timutteridge @RenskeOnstein @hsauquet_rbgsyd
