Stinging Trichomes in Apocynaceae and Their Evolution in Angiosperms

Area of Science:

• Botany
• Plant Biology
• Ecology

Background:

• Stinging trichomes are rare plant structures, documented in only a few angiosperm families.
• The Apocynaceae family, specifically the genera Fischeria and Matelea, lacked documented stinging trichomes despite anecdotal evidence of skin irritation.

Purpose of the Study:

• To investigate the potential presence and characteristics of stinging trichomes in Fischeria and Matelea species.
• To confirm if glandular trichomes in these genera function as stinging trichomes.

Main Methods:

• Microscopic analysis (light and scanning electron microscopy) of vegetative shoots and leaves.
• Histochemical tests to determine the chemical composition of trichome secretions.

Main Results:

• Glandular trichomes with a needle-shaped apex and a dilated base were found on leaves and stems.
• Secretions containing amino acids and/or proteins are released upon mechanical stimulation, causing skin irritation.
• Crystals in the cell wall facilitate trichome rupture and secretion release.

Conclusions:

• The glandular trichomes of Fischeria and Matelea are confirmed as stinging trichomes, representing the first report in the Apocynaceae family.
• This finding expands the known diversity of stinging trichomes in angiosperms.
• Stinging trichomes have evolved multiple times independently, likely as a defense against herbivores.