Unusual habitats, unusual plants—An overview of eastern Brazil’s cactus habitats

Leo A Martin & Gary James

Leo Martin and Gary James put together an overview of habitat types encountered on the CSSA field trip to Eastern Brazil. Their article in the special issue goes into more depth than on our website, but here we can offer more pictures illustrating the various habitats and some of their succulent inhabitants.

The Brazilian states of Bahía and Minas Gerais lie in the tropics south of the equator—Bahía (bah-EE-ah) on Brazil’s east coast, just south of the Amazon region; Minas Gerais (MEE-nass zhe-RICE) the next state west and extending farther south. Traveling inland from the sea, elevations rise gradually through hilly terrain, and there are numerous mountain chains and watercourses culminating in broad valleys and flat-topped inland plateaus. This diverse landscape harbors many unique habitats that support an equally unique assemblage of succulent plants, and eastern Brazil harbors over 10% of all known species of cacti.

Rain falls along Brazil’s coast at any season (although there’s more in summer), while inland most rain falls during the summer months, and winters are long and dry. And where nights are substantially cooler than days, dew is commonplace. Temperatures on the coast are similar to those in other tropical coastal areas, such as Honolulu or Puerto Vallarta: year-round warmth and humidity is the rule. Moving inland, summer daytime temperatures rise, with some areas experiencing summer temperatures exceeding 125° F and relative humidities stagnating at 99%. Nighttime in the forested middle elevations doesn’t cool off much, but temperatures plummet in more arid regions on summer nights. Inland winters feature days in the 70 to 90s, depending on elevation, and nights in the 40s to 70s. On the desert-like plateau around Diamantina, light overnight frosts are possible during the arid winter but, by and large, succulents from these states are sensitive to cold and should be kept warm year-round in cultivation.

Coastal restinga

A narrow belt of coastal sand dunes, called restinga (ress-TING-gah), has been all but wiped out by development as in most littoral habitats worldwide. We saw a number of succulents growing on and among old, stabilized dunes within a mile of the beach. Cereus fernambucensis and Melocactus violaceus ssp margaritaceus grow on the sides of dunes at the edge of dense vegetation, where they receive a half day’s sun. Pilosocereus catingicola ssp salvadorensis emerges into full sun, and Euphorbia gymnoclada also grows out in the open. Vanilla bahiensis, a vining orchid, grows under and through trees and shrubs. These plants experience year-round daytime temperatures in the 80s, with nights dropping into the 60s.

Forests

Somewhat inland dense forests once stood on flat to gently hilly terrain, almost all now cleared for sugar cane and cattle. Where they remain standing, the interplay between trees, climate, and geography determines where succulents can grow. At lower elevations nighttime temperature rarely fall below 50° F; at higher elevations the forest canopy protects plants from any chance of overnight frost.

Epiphytes

Most succulents prefer a lot of light, so few occur among stands of trees, and of those that do, epiphytes predominate. They can be low-light forest-floor dwellers and large plants that emerge above the canopy. Shade-loving epiphytes in Bahía include Rhipsalis baccifera, R. floccosa, R. lindbergiana, R. russellii, and R. teres. Some form green curtains over ten feet wide and fifteen feet long, receiving less light than any small-windowed bathroom.

Epiphytes growing nearer the canopy and at the forest edge can receive direct sun for several hours a day. Among these are orchids, bromeliads, and cacti, including. They are accustomed to receiving lots of summer rain and winter dew, so they never dry out for long in the wild. They most definitely are not desert plants and don’t survive if treated as such. In arid climates they fare best in containers, where the roots remain moist longer.

Forest Floor

The forest floor holds a few succulent surprises, such as a wonderful bromeliad, Neglaziovia variegata, which often forms dense stands in the shade of trees, resembling a tall sansevieria. Several Arrojadoa species (in Portuguese this name is pronounced ah-hoe-zha-DOE-ah) are found on the forest floor. These are small-scale columnar cacti that form terminal cephalia (densely spined segments from which flowers form) which then revert back to normal growth, producing bristly-ringed stems. We saw A. eriocaulis, A. penicillata, and A. rhodantha flowering under winter-dormant trees and shrubs. Their bright flowers were easy to spot among the dead leaves and bare plants, and hummingbirds love them.

Forest Emergent

Moving up through the forest we discover a number of “forest-emergent” succulents, which few hobbyists manage to grow to maturity. These species sprout in dense shade, grow for awhile as understory plants, and eventually grow tall enough to reach the canopy and flower. Among these is the biggest cactus we saw in Brazil: Cereus jamacaru. Widespread throughout Brazil’s deciduous forests, these enormous plant are often festooned with epiphytes, including other cacti. Locals regard this Cereus as their symbol of strength, the way US residents might regard the bald eagle.

Caatinga, forest clearings, cerrado, and grassland

Many succulents that grow at the forest margin or within a low scrub called caatinga (kah-TING-gah), a name that means “white” in reference to the sun-bleached dry-season plant stems. These areas are hot, even and winter, receive less rain, and have thinner soils with minimal water retention. Caatinga is undesirable land for agriculture, so much remains intact, although it may be grazed by cattle.

Almost no native grassland remains untrampled by cattle or goats, but a few succulents do make their home in tall grass, alongside several beautiful orchids species.

Cerrado is a fire-adapted plant community that receives plentiful summer rain followed by a long dry season, when brush fires can occur. Many plants here have underground stems or tubers that resprout after fires come through. Much of the cerrado is being cleared for enormous eucalyptus and pine plantations. The eucalyptus trees are mostly burned to make charcoal to fuel Brazilian industry, the pines tapped for turpentine.

Bare rock

Steep granite and sandstone peaks, weathered smooth, emerge above the landscape, and isolated mountains of dense, sharply-weathered bambui limestone (bam-BOO-ee) remain from epochs when this land was undersea. Occasionally, in the midst of dense forest, bare rocky slopes and domes mark spots where trees can’t grow, and here sun penetrates to the ground. These rocky habitats are relatively uncommon, so plants growing here are correspondingly rare. Some species occur only on one small exposed rock face and nowhere else. These are tough plants, growing on bare sun-baked rock where summer temperatures often exceed 120° F. But these plants receive a lot of summer rain, so they never go long without water during the hot season. Their roots are accustomed to being moist but well-aerated.

Quartz, sands, and pavements

Sandstone formations and sandy soils are probably the most widespread of the soil types we encountered. Quartz fields, with their brilliant white sand or pebbles, are well known succulent habitats in South Africa, but they are also found in many parts of eastern Brazil, where they support a unique assemblage of plants. The gloriously symmetrical and coveted Uebelmannia gummifera is one example of a quartz-dwelling cactus. It’s seeds germinate below the soil surface, where the translucent pebbles serve as tiny greenhouses. As the plantlets swell, they slow push away the greenhouse roof to emerge above the pebble surface.

Some areas are true desert, with gravel or rock pavement. A little rain falls in summer; none in winter; it is warm to hot all year. Many plants growing here are also found in caatinga or rocky habitats. Others hide in microhabitats similar to preferred, normally wetter habitats. A few plants are only found in these desert areas.