Posted on by tonytomeo · 60 Comments

Cacti Are Notorious For Nonconformity

80808thumbAlmost everyone thinks of cacti as tough plants that live out in the hottest and driest parts of the deserts, where few other plants can survive. They are the sorts of plants that we threaten to plant out in the most inhospitable or neglected parts of the garden. We never actually do so, just because we do not appreciate cacti any more than weeds. They are fine over in the neighbor’s garden.

Whether we like them or not, cacti really deserve more respect than that. Even if they do not fit our style of landscape, they are striking and distinctive features within the landscapes that they are adapted to. Except for a few euphorbs that look sort of like cacti, there are no substitutes for their form and, of course, their texture! The uniquely specialized physiology of cacti is extraordinary.

Cacti really are built for the desert. In a climate where heat and arid air desiccates foliage, cacti do without. Photosynthesis is done in the green skin of the distended stems. Furrows in the stems of some cacti increase surface area for photosynthesis, but still expose far less surface area to the weather than individual leaves would. The succulent flesh of the distended stems stores water.

The foliage is not totally lacking. It is merely modified into sharp spines or irritating glochids with which cacti protect their succulent flesh from animals. Spines of the old man cactus are elongated into coarse hair that diffuses the intensity of the sunlight that might otherwise scorch the green skin below. Bigger thorns that extend beyond the spines within each tuft are actually modified stems.

Cacti certainly put significant effort into surviving desert climates; but surprisingly, most cacti do not even live in deserts, and many live in tropical rainforests of South and Central America! Some have weirdly pendulous stem structure, and some are epiphytic, so they hang from limbs of larger trees. In regions where most insect and animal activity is at night, cacti bloom nocturnally, with big luminescent and fragrant flowers that appeal to moths, bats and their associates.

Posted on by tonytomeo · 10 Comments

Plants Are Masters Of Deception

80307thumbMany 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.