Guest AuthorFlowers, besides being lovely gifts on special occasions, are highly complex structures responsible for the reproduction of flowering plants and, consequently, the formation of fruits and seeds. Most flowering plants, known as angiosperms, are hermaphroditic, meaning that within a single flower are the structures that produce ovules – known as pistils – and pollen grains – known as stamens. As a result, in hermaphroditic plants, there is a higher likelihood that the pollen reaching the pistil comes from the same flower rather than from flowers of other individuals. This phenomenon, known as self-pollination, entails various reproductive costs that may decrease fruit and seed production, and even the genetic diversity of their populations. Despite this, hermaphroditic plants can employ different strategies to promote pollen transport between flowers of different individuals, thereby enhancing their reproductive success.
In a tropical dry forest area in Northeast Brazil, Dr. Elisângela Bezerra and her collaborators found a population of Janusia anisandra (Malpighiaceae) with individuals that appeared to have two types of flowers: some with the pistil bent to the left and others to the right, with one flower being the mirror image of the other. This floral system, known as enantiostyly, has already been reported for species from 20 botanical families that offer pollen or nectar as a reward for their pollinators, including the Malpighiaceae family. To the researchers’ surprise, J. anisandra would be the second case of enantiostyly within the Malpighiaceae family, but the first for flowers that offer oils as a reward.
To describe this floral system, the researchers studied the floral morphology, reproduction, and floral visitors of the J. anisandra population. In their study, they found that, like most neotropical species in the Malpighiaceae family, J. anisandra flowers have five petals and four pairs of oil-producing glands in the calyx, known as elaiophores. However, when they characterized the reproductive structures, they found something surprising and previously unrecorded in neotropical species of this family.
Firstly, the flowers of J. anisandra exhibited two sets of stamens, four small ones in the middle of the flower and two large ones curved at the level of the pistil. This is known as heteranthery, a floral system in which stamens can vary in shape, size, and function. Generally, the larger stamens deposit pollen in safe sites where pollinators cannot clean it, thus the pollen from these stamens plays a greater role in plant reproduction. On the other hand, the smaller stamens typically deposit pollen in locations where pollinators can clean and use it as food. Secondly, as previously observed, each flower has a single pistil, which can be bent to the left or right, forming two floral morphs that can be found within the same individual, indicating that this population exhibits what is known as monomorphic enantiostyly.
Additionally, the researchers conducted manual pollination experiments, where they took pollen from the anthers and deposited it on the pistil of the same flower or on flowers from different individuals, assessing the capacity for self-pollination or cross-pollination, respectively. They found that the species produced more fruits when they performed cross-pollination with pollen from the larger stamens, unlike when they conducted self-pollination. Therefore, the authors suggest that enantiostyly may function as an efficient strategy that reduces self-pollination and promotes cross-pollination.
This possibility became even clearer when they observed the floral visitors and potential pollinators of these plants. The researchers recorded four species of bees from the genus Centris, a group known for their close association with oil-producing flowers, as females use them to feed their larvae, construct their nests, or even as food for adults. However, due to the number of visits and their contact with the reproductive structures, they considered C. fuscata and C. aenea as the main pollinators in this population. According to their observations, when these bees visited the flowers, the larger stamens contacted the dorsal part of their bodies, leaving the pollen in safe sites where the pistils would also come into contact. What’s most interesting about this is that since there are two floral morphs, there is an increased probability that, for example, the pollen from flowers with pistils bent to the left will reach pistils of flowers with pistils bent to the right and vice versa, promoting pollination between the two morphs.
Finally, Bezerra and colleagues emphasize that this new record of enantiostyly in oil-producing flowers opens space for fascinating questions related to its evolution and function in this group of plants. This serves as an excellent example of how the different characteristics observed in the flowers of our gardens, cities, or forests can make a huge difference in how plants reproduce. Hopefully, the next time you see a flower with a feature that strikes you as curious or surprising, you might wonder: How does this influence its pollination?
READ THE ARTICLE:
Bezerra, E. L. D. S., Sabino‐Oliveira, A. C., & Machado, I. C. (2023). Janusia anisandra (A. Juss.) Griseb (Malpighiaceae): The first case of enantiostyly in oil‐flower species. Austral Ecology, 48(7), 1466-1472. https://doi.org/10.1111/aec.13402
Carlos A. Matallana Puerto is a botanist passionate about studying the floral and reproductive biology of angiosperms. His research focuses on the ecology and evolution of pollination systems in trap flowers.
Spanish and Portuguese versions by Carlos A. Matallana Puerto.
Cover Image by Ana Carolina Sabino-Oliveira.
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