abstract abundant angular appearances backdrop background banded color colored coloring colors colour coloured colouring colours contrast contrasting cultivars curved dark dark-green decorative devil's-tongue display distinctive edges erect evergreen flat foliage hardy indoor-plant long mother-in-law's-tongue mottled ornamental outdoor-plant plant pointed rigid sansevieria snake-plant snake-tongue surface surfaces texture textures thick variegated attract-prey attracted attraction carnivore carnivorous carnivorous-plants clumps clusters cover devour digest digested digesting edge enzymes flora flowers funnel herbaceous insect-trap insects nectar-like-secretions nutrient-source nutrients operculum passive-trap perennials pitcher-plants pitchers pitfall-traps plants prey proteases rims slippery species trap unusual variations variety vegetation veins