Gesneriaceae

From about 1997 onwards, molecular phylogenetic studies led to extensive changes in the classification of the family Gesneriaceae and its genera, many of which have been re-circumscribed or synonymized. New species are still being discovered, particularly in Asia, and may further change generic boundaries. A consensus phylogeny used to build classifications of the family in 2013 and 2020 is shown below (to the level of tribes). The family Calceolariaceae is shown as the sister to Gesneriaceae.[11][12]

A phylogenomic study published in 2021 which used 418 nuclear genes confirmed the monophyly of all the subfamilies and tribes. It resolved Peltanthera as sister to a clade of Calceolariaceae and Gesneriaceae. Within the Gesnerioideae, Napeantheae rather than Titanotricheae was found to be sister to the remaining tribes. The position of Titanotricheae varied according to the method used to build the cladogram, which the authors suggested was due to incomplete lineage sorting following rapid divergence. The phylogenetic position of Titanotrichum remains unsettled.[13]

The genus Sanango has not always been included in Gesneriaceae. However, molecular phylogenetic studies published up to and including 2021 suggest that it does belong in the family as the most basal member, and it is placed in its own subfamily. The studies also show the genus Peltanthera to be outside the family,[12][13] although some sources still place it within the Gesneriaceae.[14] The genus Rehmannia has also sometimes been included in the family but is now referred to the family Orobanchaceae.[15]

No single morphological feature absolutely divides two main subfamilies (i.e. forms a uniform synapomorphy). Gesnerioideae seedlings have normal cotyledons of the same size and shape (isocotylous). The cotyledons of Didymocarpoideae are usually, but not always, eventually different in size and shape (anisocotylous). One cotyledon ceases to grow and withers away, while the other continues to grow, and may even form a very large leaf that is the only one the plant has (Monophyllaea, some Streptocarpus). Gesnerioideae flowers usually have four fertile stamens, rarely two or five. Didymocarpoideae flowers usually have two fertile stamens, less often four, rarely one or five.[12]

Rhynchoglossum notonianum

On the basis of molecular phylogenetic, morphological and biogeographical differences, the family has been divided into two major subfamilies: subfamily Didymocarpoideae (formerly Cyrtandroideae) with all but one species from the Old World, and subfamily Gesnerioideae native from the Americas west through the Pacific to Australia and southeastern China. The genus Sanango is placed in its own subfamily, Sanangoideae. The two main subfamilies are further divided into tribes and subtribes.[12]

Genera accepted by Plants of the World Online (PoWO) as of April 2021 are listed below,[16] together with their placement in a subfamily and tribe by Weber et al. (2020).[12] Three genera are listed by PoWO but not by Weber et al.: Coptocheile Hoffmanns. (doubtfully placed in Gesneriaceae), Parakohleria Wiehler (now included in Pearcea) and Peltanthera Benth. (excluded from Gesneriaceae by molecular phylogenetic studies).