Adventures in 𝘉𝘦𝘨𝘰𝘯𝘪𝘢: Section 𝘗𝘳𝘪𝘵𝘻𝘦𝘭𝘪𝘢

Begonia paranaensis Brade, a species endemic to Brazil's Atlantic Forest. Photo copyright Mauro Peixoto.

 

I'm a little obsessed with begonias, but their near universal popularity with gardeners around the world suggests I'm not alone. Begonia is one of the largest and most diverse genera of any organisms, containing anywhere from 1800 to over 2,000 species depending on who you ask and many hundreds more cultivated varieties and hybrids. I plan to devote multiple articles to this beast of a taxonomic group but our adventures in Begonia begin with the section Pritzelia. A rather enigmatic group of begonias restricted to South America, the primary center of diversity for these plants is the Atlantic Forest of eastern Brazil. Doorenbos, Sosef & Wilde (1998) assigned 122 species to Pritzelia, but new species have been described in the years since. Exactly what defines a Begonia as a Pritzelia is tough to nail down. They are diverse in leaf and floral anatomy and exhibit a range of growth habits from rhizomatous creepers to shrubs and trees. The two universal features uniting Pritzelia species (according to Doorenbos, Sosef & Wilde, 1998) are placental anatomy and the presence of cystoliths in the leaf cells, despite the fact that cystoliths are not present in at least two species.

Anatomical diagram of Begonia epipsila Brade showing "typical" features of sect. Pritzelia, from Doorenbos, Sosef & Wilde (1998).

Technicalities aside, what does it mean to live life as a Pritzelia? Like most begonias, these plants are often highly endemic residents of shady tropical understories. However, as mentioned earlier, this section breaks the typical Begonia mold with the evolution of tree-like species. Among these is the remarkable B. arborescens Raddi. Referenced as one of the largest free-standing begonias (Tebbitt 2005), I cannot for the life of me find any actual size references. It is safe to assume that these are relatively small trees, standing in the humid shade of the tall canopy trees. Nonetheless, these are fascinating plants that resemble elms Ulmus spp. more than begonias. It has even been suggested that B. arborescens may mimic species of Cecropia, a large genus of tropical trees protected from herbivores by a symbiotic relationship with ants (Tebbitt 2005). 

The oddly elm-like leaves of Begonia arborescens Raddi. Photo copyright Arthur Couto from here.

Pritzelia are not commonly cultivated compared to other begonia sections, with the notable exception of B. coccinea Hook. This shrubby species (also endemic to the Atlantic Forest) has been widely hybridized to create a suite of cultivars known collectively by gardeners as "angel wing" or "cane" begonias. Deducing the actual ancestry of many domestic cultivars is nearly impossible; the world of begonia cultivation can feel mysterious and intimidating for those uninitiated. It is worth pointing out that many wild begonia species exhibit "angel wing"-like leaves and cane-like growth habits. Indeed, many members of this genus have evolved forms and patterns naturally that rival our artificially bred cultivars in their extravagance.

Begonia "Benigo Pink," one of the many "angel wing" cultivars with B. coccinea ancestry. Photo from here.

Flowers of a wild-type Begonia coccinea, from here.

REFERENCES

Doorenbos, J., Sosef, M. S. M., & De Wilde, J. J. F. E. (1998). The sections of Begonia including descriptions, keys and species lists (Studies in Begoniaceae VI) (No. 98-2). Wageningen Agricultural University.

Tebbitt, M. C. (2005). Begonias: cultivation, identification, and natural history. Timber Press (OR).