Come and Understand Flowers Through Flora Brasiliensis

Unlike ferns and pines, angiosperms have a structure called flower. The name angiosperm is derived from the Greek words “angeion,” meaning urn/vessel, and “sperma,” meaning seed, giving us hints about this group’s main feature: the seeds in urns, or fruits. There are more than 325,000 species of angiosperms, with the most varied shapes and sizes, including trees, herbs, shrubs, vines, aquatic plants, and even parasites of other plants.

What better way to understand a flower than by drawing it? Flora Brasiliensis is the largest historical work of botany in Brazil, covering 22,767 species, with thousands of illustrations. These drawings can be used to understand the diversity and variety of flower shapes.

The most visible parts of the flower are the sepals and petals, which protect the reproductive leaves and attract pollinators. In a typical flower, the sepals are the outermost part, together forming the calyx. Inside the sepals are the petals, which together form the corolla. When sepals and petals are similar, the flower is called homochlamydeous; if different, heterochlamydeous.

An essential characteristic that varies greatly in flowers is the degree of fusion of their parts. When they are fused together, we use the prefixes “gamo,” and when they are free, we say “diali”. For example, flowers with united sepals are called gamosepalous, like the Abutilon megapotamicum in this image. Typically sepals are green, but in this plant, and many others, they can be colored.

When the petals are fused, the flower is called gamopetalous; if they are free, dialipetalous.

Inside the petals are the male fertile leaves, called stamens. Their grouping is named the androecium. Stamens can be few or many, free or fused, of different heights (heterodynamous) or similar heights (isodynamous). The pollen grains, where the male gametes form, are produced at the top of the stamens. Pollinators transport the pollen from one flower to another to reach the ovary.

The innermost part of the flower contains the carpels, the female fertile leaves. In the flower, this leaf folds to protect the ovules. Its tip specializes in receiving pollen and is called the stigma; the style carries the pollen to the ovary, where the ovules with the female gametes are. After fertilization, the ovules become seeds, and the ovary develops into fruit. The number of carpels and how they fuse are vital aspects for identifying families, genera, and species.

A sequence of images shows the development of the fruit known as wild cucumber (Melothria cucumis): 1) flower with ovules attached to the ovary wall (placentation known as parietal); 2) longitudinal section of the ovary; 3) fruit development; 4) developed fruit.