Shade plants can be thought of as either providing shade or requiring some degree of shade for normal growth. Shade describes the comparative darkness at a particular location through blockage of the sun’s rays. Plants have been classified according to their optimal light requirements, those needing full sunlight for good growth are known as heliophytes (sun-loving), while those growing best in shade are known as sciophytes (shade-loving). However, some plants are more adaptable than others; there are heliophytes that will grow in partial shade and sciophytes which are not damaged by bright light.
Heliophytes are capable of a more efficient use of high light intensities than sciophytes. Heliophytes can never reach photosynthetic saturation under natural conditions; sciophytes often reach a saturation level at light intensities of only 20% of full sunlight. Heliophytes grown under shade exhibit reduced growth and reproduction. Sciophytes placed in the direct sun can experience leaf burn and wilting. In a shaded environment, sciophytes have developed large leaves with large surfaces containing a high concentration of chlorophyll and accessory pigment. Photosynthesis in such plants make the best use of light available from sunflecks and reflection.
A tropical rainforest is an excellent natural example of how sun and shade plants coexist, and its vertical structure can to some degree be replicated with garden plants. Four distinctive layers are found in a mature tropical rainforest. Topmost is an emergent discontinuous layer of heliophytic trees, up to 200 feet tall with umbrella-shaped crowns. Next is the canopy layer of continuous tree crowns, with trees 60-90 feet tall, predominantly heliophytes. The canopy also contains numerous ground-rooted vines and is rich in animal life, especially birds. The understory layer is heavily shaded, receiving 15 percent or less of the sunlight able to filter through the canopy. Tree growth is not continuous and is composed of tree species waiting to take their place in the canopy or emergent layers, as older trees die and fall, creating a gap in the canopy. These understory trees undergo a growth spurt when more light becomes available. Orchids, bromeliads and other schiophytes are common to this layer. The understory is hot and damp, and rich in animal life, particularly insects. The forest floor layer is almost complete shade. Small seedlings and saplings and other plants are sparsely scattered around so that it is possible to walk about. A considerable amount of litter is present but it decays quickly under the hot, humid conditions; ground animals, ants and other lifeforms are present. One of many fascinating adaptations of plants in the tropical rain forest is that on the forest floor, where canopy vine seeds are dropped, they germinate and become sciotrophic, growing toward the darkest object, which is the trunk of a tree. When they start to climb the tree they change and become heliotrophic, growing upward toward the light in the canopy.
The creative gardener can create a pleasing combination of sun and shade plants, including trees, shrubs and herbaceous plants, by taking into account the way nature has structured tropical rainforests. The trees and shrubs in the TreeWorld inventory are labeled with regard to light requirements, making species selection easy.