Houseplants in the Wild
Even an extensive library cannot serve as a substitute for the knowledge gained by a few weeks’ stay in the tropics and subtropics so let us make a brief excursion into these realms; let us take a look at how our green friends live.
Let us start in Ecuador, by the small river Rio Negro, tributary of the Pastaza, which in these parts widens and flows slowly towards the Amazon region. The altitude above sea level is no more than 600 m (2,000 ft), the temperature constantly high, and the humidity likewise. Only at night does the temperature drop to a ‘mere’ 15°C (59°F), which means that the vegetation is drenched with dew in the early morning. The dew, however, does not remain long on the leaves. Many tropical plants have smooth, waxy foliage, off which the water quickly runs. Also, leaves often terminate in a tapering point which enables a quick run-off of water from the leaf blade. The well-known rubber plant (Ficus elastica) has leaves such as this, and here on our excursion we find them on Philodendron verrucosum, one of the most striking plants of the local undergrowth. It grows on the banks of the river in damp places rich in humus and some older specimens climb like lianas up the trunks of neighbouring trees to weave an impenetrable canopy of green above the stream, together with yams (Dioscorea polygonoides and D. trifida) and members of the Vitaceae and Leguminosae families, beneath which permanent twilight reigns. In the undergrowth we will find many plants that we recognize as familiar house plants. At the edge of the forest is Costus comosus, a few paces farther the robust Heliconia wagneriana and at its base a lovely begonia growing in the deep shade.
The smooth trunks of the trees are not devoid of life. Several bromeliads are found attached to them, their leaves forming funnels which hold water from the morning dew as well as from the previous evening’s rainfall, thus not only providing a reserve supply for the plant’s use but also serving as ‘hanging pools’ in which small tree frogs can rear their offspring. The water in the funnels of bromeliads is also inhabited by the larvae of mosquitoes and other insects. This is of advantage to both partners: the animals have an assured supply of water and the remains of the animals’ bodies provide the plants with organic matter which they would otherwise find difficult to obtain high up above the ground. Their roots serve only as anchorage, they are stiff and wiry and merely hold the plant to the bark. Food and water are obtained mainly through the leaves.
Other plants that have caught a foothold in the cracked bark of the tree include various members of the genus Peperomia, which are compact in habit and far prettier in their natural habitat than when grown in the home, where they generally become tall and spindly. Orchids are to be found here too; one that is easily recognized from afar is Oncidium varicosum with its sprays of golden-yellow. The tuft of roots faces upwards, thus catching every falling leaf and every stone dropped by an ant or termite on its way up the tree trunk. Over the years the orchid thus collects a small amount of humus on which to feed. A little nourishment is also obtained from the dust captured by rain. Traces of this humble diet are absorbed through the velamen, the corky outer layer of the aerial roots.
Returning to the river where marantas grow in the damp and shade amidst selaginellas and mosses, let us follow it down to the road. On the steep road bank, about 2 m (6 ft) high, grows a bromeliad of the genus Pitcairnia. It grows in the ground and its roots have retained their function. It is also equipped for unexpected periods of drought, not with a rosette of leaves, as are many plants, but with a kind of bulb at the base of the leaf. Its beautiful flowers, not very long lasting, were at one time considered the loveliest of the whole family. Another lovely plant growing by the roadside that attracts our notice is the large-leaved Anthurium, its leaves hanging freely down the almost vertical bank. Anthuriums, with their long-bladed leaves, (the blades are often longer than the leaf stalks) are either epiphytic or grow on steep rocks, often covered with moss, down which water continues to run a long time after it has rained. The sodden moss thus supplies the required moisture to the roots. It is definitely a mistake when these plants are grown in open beds in botanical gardens, for the leaves often rot when the leaf tips touch the ground.
We shall now make our way to the border of North and Central America, to a land that has provided horticulture with many magnificent plants — to Mexico. We are in the semi-desert near the city of Tehuacan in the state of Puebla, about 1,670 m (5,500 ft) above sea level. Let us imagine that we have arrived at this spot in October, in other words after the summer rains, and are greeted by fairly lush vegetation. The shrub Gymnosperma glutinosum is bright with yellow blossoms, the cacti are in flower too, particularly striking being the giant cushions of Ferocactus robustus composed of hundreds of individual specimens. There are many other cacti growing here, such as cylindopuntias and mammillarias. The other vegetation is also xerophilous, in other words, able to withstand long periods of drought.
Creeping along the ground is a short-stemmed plant with only a few leaves — a member of the genus Cissus. Plants of the same genus growing in the tropical rainforest are quite different: their leaves are large, thin and brightly coloured, whereas those growing in semi-deserts have small, fleshy leaves covered with a thick grey felt. The greatest surprise, however, is the difference in the root system. That of the 11 tropical species growing in permanently moistis comparatively shallow, whereas in the semi-desert species, which has to make the most of every drop of water that rapidly soaks into the gypsum-rich soil, the roots grow from a huge underground (huge, that is, compared to the size of the aerial parts). The same disproportion between the top and underground parts may be found in many other succulents and cacti.
We may also come across bulbs of the genus Zephyranthes which have already had time to die back since the rainy season. They belong to the group known as ephemeral plants which have a brief life cycle — germinating, flowering and producing seeds during the brief growing season and waiting out the unfavourable, usually dry season either in the form of seeds (annuals) or as latent buds or tubers.
In the awesome landscape of the semi-desert, dominated by yuccas, agaves, Beaucarnea gracilis and other plants of this type, we will also encounter flowering annuals that are popular garden plants — the ubiquitous tagetes, and on sun-baked rocks zinnias, their red flowers just fading so that they can form seeds in time. Epiphytes are to be found here, too. Growing on an old woody opuntia is the bromeliad Tillandsia capillaris. It is one of the least demanding of plants. Protecting it from the sun is a silvery coat of scales that catches every drop of moisture, both from rain and night-time mists, passing it to the cells in the inner leaf tissues. The leaves are long and narrow, and round in cross-section so that evaporation is kept to the minimum. We can even see this plant growing in clumps on telegraph wires. How it must economize with food and water in such conditions! All plants, of course, have to economize with water here. Many mechanisms for trapping water were not discovered until fairly recently. The spines of many cacti, for example, are capable of catching tiny droplets of water from mist, absorbing them and passing them on to the storage tissues inside the plant.
The semi-desert of Mexico that we have been referring to has a low annual rainfall, approximately 48 cm (19 in) with a maximum of 12 cm (4-3/4 in), a minimum of 0.2 cm (1/8 in) per month, and a comparatively stable temperature — the mean annual temperature is 18.6°C (65°F) with a minimum of 15°C (59°F) and maximum of 21.5°C (71°F); of course the difference between day-time and night-time temperatures is very great. These figures indicate that it will not be difficult to grow the plants of this area in the modern household if they are provided with ample light on a window-sill facing south.
The last place we shall visit is the Vietnamese village of Tarn Dao (altitude about 1,000 m [3,300 ft] above sea level), located some 100 kilometres (62 miles) north of Hanoi. The mountains are covered with dense forest, which may be characterized as a transitional form between the lowland tropical areas and the evergreen subtropical regions. The main characteristic is ample moisture in the form of mist and lower temperature throughout the year, but never less than 10°C (50°F). The forest consists of a great variety of trees and shrubs, mostly of the family Dipterocarpaceae, and the genera Castanopsis, Podocarpus and Bucklandia. Here, too, we will find countless epiphytes on the trees. Not bromeliads, of course, for these are almost totally restricted to the American continent, but ferns of the genera Pyrrosia and Drynaria, orchids of the genera Dendrobium, Bulbophyllum and Coelogyne and the typically Asian epiphytic genus, Aeschynanthus. Also worthy of note are the banks of the stream where sweet flag (Acorus gramineus) forms a thick cover on the damp stones (contrary to the widely held belief that it grows in mud). The trees are not inhabited only by epiphytes but also serve as a support for countless creepers. These include Rhaphidophora decursiva and other species of the same genus, numerous members of the genus Pothos, Ficus pumila and many members of the vine family such as cissus, ampelopsis, vitis, tetrastigma and cayratia. Impressive and stately are the tree ferns, Cyathea spinulosa, reaching a height of almost 3 m (10 ft). In dark places in the forest undergrowth we will find selaginellas and ferns, in lighter spots begonias and in sunlit places the well-known gynura, with its gleaming violet hairs (trichomes). Characteristic of Tarn Dao, however, are plants of the Araliaceae family, be they the comparatively large and well-known species of the genus Schefflera, or the delicate but sharply-spined Aralia armata. Near the village there are also several specimens of the shrub Tieghemopanax fruticosus; these have probably escaped from gardens and become naturalized but, as one can see, they have found conditions here to their liking. Some plants strike one as odd that they have not yet been introduced into cultivation. It is hard to understand, for instance, why a magnificent foliage plant such as Ficus semicordata has remained unnoticed, though it might do quite well as a house plant. If we stop once again to consider the possibilities such a locality offers to horticulture then we find that many of the local plants could perhaps be grown successfully in the modern home if the leaves were sprayed over every now and then or if the atmos-pheric moisture was slightly increased.
Let us hope that this excursion into the realm of plants and their native habitats has not tired the reader but, on the contrary, has awakened his desire to go out after them into the wild himself. If so, then it will be useful for him to know how to take plants and their seeds home with him without damaging them on the way or how to bring home a plant that does not have ripe seeds when discovered.