Mustard’s flowers are bright yellow crosses. (BIGSTOCK)

Call it an odd blend of sex and religion, but a good many plants in our garden make the sign of the cross when they bloom.

Botanists classify most flowering plants according to the form of their flowers, and the vegetables in the family Cruciferae, which means “cross-bearing,” are named for their cross-shaped blossoms, made up of four symmetrical petals. They’re sometimes referred to as crucifers, and often as brassicas, since most are in the genus Brassica. Those include cabbage, kale, collards, broccoli, Brussels sprouts, cauliflower, Chinese cabbage, mustard, rutabagas and turnips. Non-brassica crucifers include horseradish, arugula, radish and cress.

Gardeners are not exactly reverent when these flowers appear, because it means that the plants are getting down to the serious job of reproduction. For us, the flowering signals a decline in what we want these vegetables for: the formation of firm round cabbages, compact broccoli heads, or lush kale and arugula leaves for cooking and salads. Rows of broccoli with flying masses of yellow blooms like flags label the gardener as a sloven who doesn’t tend to the garden by picking regularly, and by removing bolted plants when their time is up.

For the bees, on the other hand, this is a great moment. Flowering crucifers are gold to them, and they will love your garden if you let some of these plants bolt, from late spring to late fall. Bees are wedded to this flower form by millennia of co-evolution, so that by burrowing into the blossoms’ reproductive centers, they might nourish themselves and their hives with nectar and pollen, and while doing so, fertilize the flowers and spread the plants’ genetics around. That golden X marks the spot where they must land. Chances are, other plants are blooming in your yard at the same time, but crucifer blossoms are especially rich treasures, and the presence of bees will help ensure the pollination of many other crops besides these.

To best nourish ourselves with our gardens, there comes a time, especially in warm summer weather, when bolted early-planted brassicas must be yanked to make room for new crops. Fall carrots, fall spinach and fall lettuces will start to go in soon, to mature in cooler weather. Fall brassicas will be planted in spaces vacated by non-brassicas, for proper crop rotation. But consider keeping a few of the flowering old ones for the bees, and while you’re at it, take a good look at the subtle differences among them. Mustard makes bright yellow crosses; broccoli’s are a bit paler yellow. Arugula’s are quite large and a lovely cream color. A few years ago I let a planting of a brassica called Happy Rich, a cross between Chinese broccoli (gai lan) and western broccoli, go magnificently to seed. It bore clouds of lush, snow-white blooms.

Do you need still another good reason not to rush such a display to the compost pile? Here’s one: Any cruciferous flower is edible and makes a dainty garnish for a salad — in any season.

Damrosch is a freelance writer and the author of “The Garden Primer.”