Stigma

Botanical stigmata are part of the female reproductive system.

Closeup of stigma surrounded by stamen of White Lilium ‘Stargazer’ lily (Subhrajyoti07) CC BY-SA 4.0

Tiny stigmata may not grab your attention at first glance, but maybe they should.

Before we learn why, let’s do a quick review of flower anatomy.

Flower anatomy

Flowers can be male, female, or both. The stigma is found in female flowers. The reproductive portion of female flowers is called the gynoecium, or ‘women’s house’. Within the gynoecium is the pistil. The pistil has three parts: the stigma, style, and ovary. The style is a long, tubelike structure that leads to the ovary. The stigma has a sticky tip, which is where pollen is received.

​Stigmas and pollination

Parts of a flower (Wikipedia) CC BY-SA 3.0

Carried by insects, bats, or wind, pollen is received at the stigma by sticky, specialized cells (stigmatic papillae). Once the pollen has been captured, the stigma, which is often quite moist, helps to rehydrate the pollen after its lengthy travels. Once hydrated, the pollen grain germinates, sending a pollen tube down the style to the ovary. To ensure that the proper pollen is collected, stigmas have evolved some very fancy attraction and capture methods.

You may be surprised to learn, as I was, that high temperatures, usually above 104°F, for 2 or more days prior to pollination, can exhaust the stigma of tomato plants to the point they cannot capture pollen. This may explain why, during particularly hot summers, we see lots of tomato blossoms, but no fruit. High temperatures (above 100°F) also reduces pollen germination.

Delicate nectarine blossom stigmas

Specialized stigma

Besides being sticky, stigmas use various shapes, flaps, and hair arrangements to help ensure that the correct pollen is captured and all others are rejected. These shapes can be simple tubes, truncated tubes, threadlike, bulbous, conical, lobed, feathery, hairy, beaked, fan-shaped, brush-like, leaflike, or disc-shaped. The familiar threads found on ears of corn, called silk, are stigmata.

Corn stigmas, or ‘silk’

Saffron crocus with yellow stigma and orange saffron threads

The long, bright orange stigmata of autumn crocus are harvested as one of the world’s most expensive spices: saffron.

​How many different stigmata shapes are there in your garden?