Mount Ayanganna bonnetia (Bonnetia ayangannensis) from the Pantepui of western Guyana, South America

NEWS - Researchers describe Mount Ayanganna bonnetia (Bonnetia ayangannensis) from the summit of Mount Ayanganna tepui in Guyana, in terms of morphology, distribution, micromorphological characterization under scanning electron microscopy, leaf venation and comparison with closely related species.

Bonnetia Mart. is the most representative genus of the woody flora of Pantepui and one of the groups with the greatest endemism in the local flora. The genus has 32 species currently known in tropical America. This study adds Bonnetia ayangannensis and the number of endemics in Pantepui to 27 species.

Micromorphological analysis of the leaves shows serrated margins, sometimes with deciduous spinular protrusions. The abaxial leaf surface is rough and has numerous sessile glands and stomata. At higher magnification, the surface appears warty-crusty with granular protrusions.

The margins of the bracts have short-stalked glands with thin-walled elongated heads. The petals have short-stalked glands on the outer surface and short-stalked glands on the margins. Seeds have longitudinal stripes.

B. ayangannensis closely resembles B. paniculata, but differs in leaf blades (1-)1.5-4 cm (vs. 6-18 cm), leaves with glandular punctuations on abaxial surface (vs. glands absent), bracts 2-3 mm (vs. 6-7 mm), sepals ciliated and glandular (vs. ciliated and glands absent) and 2-4 × 1-2 mm (vs. 10 mm × 6-7 mm).

B. ayangannensis differs from B. tepuiensis and B. rubicunda by having leaves that are wedge-shaped at the base (vs. rounded in B. tepuiensis), stalked flowers (vs. sessile), arranged in inflorescences (vs. solitary flowers), pinnate venation, flowers with sepals and petals less than 8 mm long (vs. parallel venation, sepals and petals more than 18 mm long in B. rubicunda).

The epithet refers to Mount Ayanganna, where the new species was discovered and is known only from two collections collected at close range from a single population on the eastern summit slope. It occurs in scrub forest on sandstone, together with B. tepuiensis, Clusia spp. and Brocchinia spp. at elevations of 1900-2000 meters.

The researchers recommend B. ayangannensis be placed in the Critically Endangered category. The species is primarily known from two locations separated by only about 0.06 km over an area of 4 km2. However, considering that at 1900 meters the actual area is thought to be much smaller. In addition, anthropogenic climate change is a serious threat to habitats in the highlands.

Original research

Barbosa-Silva RG, Torke BM, Viana PL (2024). A new species of Bonnetia Mart. (Bonnetiaceae) from the Pantepui of South America. PhytoKeys 247: 55-65, DOI:10.3897/phytokeys.247.126950

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