all-weather-space Apocynaceae bark caudex caudiciform-plant conservatory display displayed distinctive dome exotics fat-twisted-roots flower-dome fockea-edulis gardens Gardens-by-the-Bay glasshouse gnarled greenhouse grotesque ground-level horticultural horticulture Hottentot-bread indoors plants semi-deciduous shape shaped shapes Singapore South-Africa-native succulent surface surfaces texture textures tree trunk unusual utilitarian vegetation vine-branches