Ask Mr. Smarty Plants

In severe climates plants are restricted in form and size. In places that are very cold, such as the Arctic tundra, Antarctic tundra or alpine tundra (high mountain elevations), plants are generally low and very compact (ex. Silene acaulis (moss campion)). This protects them from the weight of snow during their long winter and, after the snow has melted in their brief summer, it protects them from cold winds. Additionally, low, clumped plants have a warmer microclimate from the sun heating the ground near them. These tundra regions have no trees or other large plants because the growth period is too short to support extensive growth. Grasses and sedges are a large component of the plants that grow there. You can read more about the tundra and the plants that grow there. Click here to learn about the two species of flowering plants that grow in Antarctica. Some plants in the alpine tundra have another adaptation to protect themselves from the high levels of ultraviolet (UV) light in the thinner atmosphere of higher elevations. UV is harmful to chlorophyll and delicate cellular structures that the plant needs to photosynthesize. There are two protection strategies: 1) the plants are covered with dense white hairs that filter the sunlight, (ex. Phacelia sericea (silky phacelia)) or 2) they have a dark red pigment called anthocyanin which absorbs the UV rays before they can harm the cellular components (ex. Saxifraga flagellaris (spider plant)).

The other notable extreme climate is the hot desert. It is the temperature combined with the scarcity of water that causes the problem. The forms adopted by plants in the desert are geared to conserving water. In the desert most of the rain comes in the wintertime and during the heat of summer with no rain plants have to conserve all the water that they can. Most desert plants put on new growth only in the spring. This is also when they carry out photosynthesis and the food they make is stored in their roots. Some perennials (ex. Fouquieria splendens (ocotillo) have very small leaves to minimize water loss that they lose in the summertime and become dormant to conserve water. Other perennials are very have thickened leaves and grow small and close to the ground (ex. Chaetopappa ericoides (rose heath). Still other perennials, such as the Carnegiea gigantea (saguaro), have no true leaves. Their stems, where photosynthesis occurs, are covered with a waxy cuticle to retain water and are pleated so that the ridges shade part of the stem. They store a great deal of water in their stems and these pleats allow the stems to expand when water is available to store. Annuals also tend to be small and flower quickly after a rain (ex. Abronia villosa (desert sand verbena). They exist mostly as seeds waiting for the next combination of rain and temperature to allow them to complete their quick life cycle and make seeds for the next generation. Plants have small openings called stomata on the undersides of their leaves (and sometimes on their stems like the saguaro) to allow for gas exchange—plants need carbon dioxide (CO2) for photosynthesis and they release oxygen (O2) as a by-product. When the stomata are open for gas exchange, however, they can also lose water. Therefore, most desert plants tend to have their stomata open only at night when it is cooler and less evaporation can occur.

You might like to see if your library has this young person's book, Plant Survival: Adapting to a Hostile World by Brian Capon to read more about how plants are adapted to different climates.

Silene acaulis

Phacelia sericea

Fouquieria splendens

Chaetopappa ericoides

Carnegiea gigantea

Abronia villosa