Microscopic analysis of ancient plant fossils reveals that early land plants were producing protective surface resins as far back as the Middle Devonian period, long before the emergence of conifers.
Researchers examined fossilized plant cuticles from Middle Devonian coals, dated to around 382 to 387 million years ago, collected from various sites in China, including regions in Yunnan and Xinjiang provinces. These cuticles, which once covered the aerial parts of early terrestrial plants, varied in thickness and came from a diverse group of herbaceous species like Rhyniophytes, Protolepidodendron, and Drepanophycus.
The team used techniques like scanning electron microscopy and gas chromatography-mass spectrometry to study the cuticles. They discovered thin organic films coating the surfaces, which fluoresced brown under UV light and dissolved in organic solvents. These films turned out to be fossilized resins, dominated by nonvolatile tetracyclic diterpenoids such as beyeranes and atisanes.
“Here we show that abundant diterpenoid-rich surface resins were already widespread on Middle Devonian plant cuticles, substantially extending the geological record of plant resin production,” the researchers report.
Unlike internal resins found in later trees, these were surface resins secreted externally, likely from glandular trichomes — hair-like structures on the plant surfaces. Evidence includes preserved trichome imprints and perforations in the cuticles, as well as larger tubercles that may have aided secretion.
The resins formed protective layers, hardening in air to shield against water loss, UV radiation, and heat. Thicker cuticles, often from sun-exposed parts, had correspondingly thicker resin films, suggesting an adaptive response to arid conditions during early land colonization.
“These surface resins, preserved alongside plant cuticles, are rich in nonvolatile tetracyclic diterpenoids and likely played a crucial role in facilitating terrestrial colonization by forming an antitranspirant barrier on the surfaces of early herbaceous plants,” the team explains.
This finding challenges previous ideas, as resins were thought to first appear in gymnosperms during the late Carboniferous, about 300 million years ago, and surface resins were linked only to flowering plants. Instead, these ancient herbaceous plants produced them much earlier, hinting at an evolutionary shift from surface coatings to internal systems in later gymnosperms.
“The identification of surface resin in Middle Devonian plants is both remarkable and unexpected. This discovery not only pushes back the timeline for the emergence of the earliest resin-producing plants but also overturns the longstanding view that surface resins were produced exclusively by angiosperms,” the researchers note.
Citations
D. Song et al. Abundant surface resins present on Middle Devonian land plants. Communications Earth & Environment. Published online January 7, 2026. DOI: 10.1038/s43247-025-03161-9
