Plant Physiology Can Be Deceiving

plant physiology
Each daisy is a composite flower.

UNITED STATES—Many of us already understand that daisies, sunflowers, asters and all related flowers are composite flowers, which bloom as many tiny flowers clustered tightly together to form what appears to be significantly larger single flowers. Distended ‘ray’ florets around the edges imitate petals that other types of flowers are equipped with. It is like one stop shopping for pollinators craving nectar.

Many other plants have developed comparably ingenious techniques for facilitating what they need to do. Flowers are the more common beneficiaries of their creativity. Fruits, leaves, stems and roots have also been modified out of necessity. For example, the colorful bracts around tiny poinsettia and bougainvillea flowers are modified leaves that pretend to be petals to attract pollinators.

We think of strawberries, pineapples and figs as fruit. Strawberry fruits are actually the small specks on the outside that resemble seeds. The sweet and juicy part that suspends these fruits is a modified stem. Each ‘eye’ of a pineapple is a swollen flower, that is fused with flowers around it. Tiny fig flowers bloom and produce seed all within the fleshy floral structure that is eaten like fruit.

Some types of acacia trees have no real leaves. Their foliage is comprised of distended petioles (leaf stems) known as ‘phyllodes,’ but without the leaves that petioles normally support. Juvenile leaves that actually look like lacy acacia leaves do not last long. Makrut lime has big phyllodes too, but in conjunction with leaves, which is why they seem to have double leaves joined end to end.

Cacti and the euphorbs (poinsettia relatives) that resemble them are among the most deceptive of plants. Euphorbs that have both recognizable leaves and thorns provide hints about how they work, since some tufts of thorns and spines also have leaves. Each tuft is a node. Small bristly spines are modified leaves. Larger and stouter thorns are modified axillary stems. A few stems develop into limbs or segments. Without leaves, the fleshy green stems do all the work of photosynthesis.

Highlight: Transvaal daisy

There is some controversy about the identity of the flowers that Mickey Mouse picks at the porch to present to Minnie Mouse when she answers the door. Some insist that they are Transvaal daisy, Gerbera hybrida. When they are not in black and white, the substantial daisy flowers are cartoon hues of yellow, orange, red, pink and white, sometimes with chocolatey brown or black centers.

Transvaal daisies are always available as cut flowers, but bloom best in cool spring and autumn weather in home gardens. Most garden varieties have single flowers on bare stems. Most cut flowers are semi-double. Double flowers that resemble zinnias, and spider flowers that resemble spider mums, are rare. Coarse basal foliage gets almost a foot high and a foot and a half wide.

Because the foliage is so vulnerable to snails, Transvaal daisy is usually grown in pots rather than in the ground or immobile planters. Besides, potted plants can be brought into the home or put in prominent spots while blooming, and then put out of sight between bloom. Transvaal daisy wants partial shade, regular watering and occasional feeding. It can take full sun exposure if not too hot.

Horticulturist Tony Tomeo can be contacted at