Flower Bud Fossils from the Early Cretaceous

The world is filled with a wide variety of flowers. Most of them possess brilliant colours, which attract attention and make them among the most admired ornamental plants.

Flowers are the defining feature of angiosperms. The global success of angiosperms today is largely tied to the evolution of the flower itself. Many flowering plants rely on insects for pollination, and in order to attract these visitors, insect-pollinated flowers evolved a remarkable diversity of colours and visual signals.

At present, the earliest known angiosperm fossils date back to the Jurassic. Most researchers agree that angiosperms began to diversify during the Cretaceous and eventually became a dominant plant group. In the Early Cretaceous Yixian Formation of Liaoning Province in China, numerous fossil flowers have previously been discovered. However, these fossils differ from the insect-pollinated flowers commonly seen today. They generally lack petals and therefore would not have displayed the bright colours typical of modern flowers. Such fossil evidence suggests that the reproductive strategies of early angiosperms were different from those of most living flowering plants.

Specimen of Archaebuda lingyuanensis（圖片來源：Chen, L. J., Wang, X. (2022) .，採用 CC BY 4.0 授權。）

In 2022, researchers described a fossil flower bud from the Yixian Formation and named it Archaebuda lingyuanensis. This specimen preserved only the external morphology of the bud, while internal structures were not visible. Because of this limitation, uncertainty remained about whether it truly represented a flower bud. In 2024, another fossil flower bud from the Yixian Formation was described. Detailed analysis demonstrated that it belongs to the same genus as Archaebuda lingyuanensis. Consequently, the specimen was described as a second species of the genus, Archaebuda cretaceae. This fossil preserves not only the pedicel and petals but also the gynoecium and possible androecium. These features confirm that flowers with petals existed in the Early Cretaceous Yixian Formation. The bud itself measures about 2 cm in length, and the fully opened flower may have been even larger.

Specimen of Archaebuda cretaceae. (a) General view of the specimen. (b) Enlarged view of the boxed area in (a), showing the morphology of the gynoecium. (c) The tip of the flower bud, showing the margins and textures of the petals（圖片來源：Huang, W., Wang, X. (2024). ，採用 CC BY 4.0 授權。）

For a long time, no fossils of large flowers were known from the Early Cretaceous. Combined with the substantial differences between early fossil flowers and modern ones, this absence led some researchers to propose that modern flowers evolved from contemporaneous naked flowers lacking petals, or from later-appearing miniature flowers with diameters of only about 0.5 to 5 millimetres. The discovery of large flowers such as Archaebuda cretaceae suggests that this view may not be reliable. The origin of modern flowers therefore remains an open question requiring further investigation. Since large flowers are now confirmed to have existed in the Early Cretaceous, researchers believe that more attention should be directed toward Jurassic angiosperm fossils.

So far, only three confirmed flower-bud fossils have been discovered. In addition to the two species of Archaebuda, the third is Florigerminis jurassica, found in Jurassic strata of Inner Mongolia. This fossil preserves not only a flower bud but also leafy branches and fruit attached to the same specimen, revealing plant organs at different stages of development. Such preservation is extremely rare in the fossil record.

Specimen of Florigerminis jurassica, showing the branch, flower bud, and fruit structures（圖片來源：Cui, D. F et al. (2022). ，採用 CC BY 4.0 授權。）

Compared with the Jurassic flower bud Florigerminis, the Early Cretaceous Archaebuda species are much larger. The bud of Florigerminis measures only 3.8 × 3.3 millimetres, whereas the bud of Archaebuda is about 20 × 9 millimetres. Even the fruit of Florigerminis is smaller than the bud of Archaebuda. This striking size difference clearly cannot be explained by developmental stage alone; rather, the flowers of Archaebuda were inherently larger and more conspicuous. Although it is currently impossible to determine whether the petals of Archaebuda were brightly coloured, large petals in living angiosperms are often associated with insect pollination. This observation suggests that mutualistic relationships between flowers and insects may already have begun forming in Early Cretaceous ecosystems, possibly even earlier than the fossil record currently indicates.

Past studies frequently emphasised the enclosure of ovules as the defining feature of angiosperms. In contrast, the functional roles of structures such as sepals, petals, or the corolla have often received less attention. In reality, the stamens and pistils inside flowers are fragile and metabolically active structures that could easily become targets for insects or other animals seeking food. The protective layer formed by petals therefore serves not only a display function but also helps shield the reproductive organs. This dual role likely provided a significant evolutionary advantage for angiosperms. Discoveries of additional fossils in the future may clarify the importance of petals in the early evolution of flowering plants.

Flower buds are rarely reported in fossil studies, probably because they are less likely to be preserved. However, this scarcity may also reflect methodological biases in traditional palaeobotanical research. As excavation efforts increase and new technologies are introduced, fossil flowers buried within sediments may become easier to detect and study. These advances could greatly improve our understanding of fossil flowers and of angiosperm evolution as a whole.

At the same time, researchers must remain cautious. Some techniques generate extremely large datasets that may subtly influence or even mislead interpretations, much like the biases discussed earlier. For this reason, palaeobotanical research should ideally employ multiple complementary methods so that results can be cross-checked and balanced.

Finally, the discovery of two species of Archaebuda within the same geological formation demonstrates that Early Cretaceous angiosperms already possessed large flowers. Together with the presence of contemporaneous flowers lacking petals, these findings reveal that floral diversity had already become far more extensive than previously assumed by about 125 million years ago.

Large flowers with conspicuous petals may have facilitated the spread of certain early angiosperms and hint that ecological interactions with animals—especially insects—were already developing at that time. Future discoveries of additional flower buds and other angiosperm fossils will help clarify the true course of early angiosperm evolution.

Author: Bai Leng

Reference:

Huang, W., Wang, X. (2024). Flower Buds Confirmed in the Early Cretaceous of China. Biology.