When choosing some foliage specimens to show to a group last week, I noticed there were a number of plants in my garden that have leaves that are green, grey or silver on top but have reddish or purplish undersides. I love this bicolour effect, especially when the plants hold their leaves at an angle whereby the undersides can be seen as well as the top of the leaves, giving quite a dramatic look. Interestingly, all the plants exhibiting this characteristic are growing in the shadier parts of my garden.
It turns out that this feature is an adaptation of plants to shade: the red or purplish underside of the leaf allows light energy falling on the leaves to reflect back into the photosynthetic tissue in the foliage rather than pass straight through it - it sort of functions like a mirror and gives the chlorophyll a second chance to utilise the light.
I enjoy grouping some of these plants together, as well as using them to create 'colour echoes' with other nearby plants. I have written previously about the concept of colour echoes: creating colour harmony and cohesion in the garden by combining two (or more) plants together that share a colour but have some other difference. For example, you can repeat the flower colour of one plant with a nearby plant that has foliage (rather than a flower) of a similar hue. Or pair a flower of a certain colour with a similarly hued bloom with a contrasting shape. Other techniques are to match the colour of a flower's bracts, calyces or central eyes to a nearby petal or leaf, or to place a flower nearby a garden sculpture, ornament or piece of furniture of the same colour. In the case of my green and reddish/purple foliaged specimens, one can pair them with plants with leaves all coloured reddish or purple, or match them with a shade-tolerant plant with a flower of such hues.
One of the most striking examples of this sort of foliage plant is Ctenanthe setosa 'Grey Star'. This is a tall perennial (ht 1.2 m) from the Marantaceae family, with elegant oblong leaves coloured silvery-grey on their upper surface and richly marked with dark veins, with deep purple undersides to the foliage. It is perfect for filling a dry corner under trees or masking unappealing fences. I enjoy it with an underplanting of similarly toned Tradescantia 'Zebrina'. It also look good grown with plants of a similar bold foliage shape but coloured all-green: such as Aspidistra and Spathiphyllum. Ctenathe oppenheimiana 'Tricolor' (ht 60 cm or more, pictured at the start of the blog) has irregular creamy white blotches on grey-patterned green leaves and distinctive cerise undersides. I have paired this with Iresine herbtii 'Brilliantissima', which has foliage of exactly the same cerise colour, to form a pleasing pair. Both these Ctenanthe plants form good clumps. The related genus Calathea (ht 40-90 cm)has some beautiful species and cultivars with purple undersides to the attractive leaves, such as Calathea lancifolia.
Many Begonia plants also have this distinctive leaf colouration - and it can be seen in various cane, shrub, rhizomatous and bedding types. The so-called 'beefsteak' rhizomatous Begonia 'Erythrophylla' is a well-known example, with its shiny, rounded, succulent green leaves that are vibrantly coloured reddish-brown beneath. I have often admired a clump of this groundcover grown with the reddish-flowered form of the shrimp plant (Justicia brandegeeana), in a garden in my suburb. The foliage of Begonia plants can be as attractive as their blooms!
Another groundcovering specimen with foliage that has coloured undersides is the cultivar 'Purple Dragon' of the succulent Crassula multicava (ht 25cm). This is an easy-going groundcover plant with plump, round leaves: green on top and purplish-red underneath, and it quietly colonises any unhospitable position in shade. In late winter and spring, it is completely smothered in a lovely fine mist of tiny white stars which open from pink buds held above the foliage.
Some Plectranthus also have attractive dark undersides to their leave. Plectranthus ciliatus is a groundcover plant, growing to 30-40cm tall. It has an autumn veil of long spires of dainty lilac-tinged flowers across its purple-veined and purple-backed leaves. It will grow in the most uncongenial shady places and can form a dense carpet under trees or shrubs, and is stunning when in full bloom. It associates well with shade-loving, dark purple-leafed foliage plants such as bromeliads, Tradescantia pallida 'Purple Heart' or black taro (Colocasia esculenta 'Black Magic') to echo the hue of its leaves' undersides. The cultivar Plectranthus 'Nico' looks like a larger-leaved version of Plectranthus ciliatus, with very striking purple veins in its textured foliage, and more distinctly coloured undersides, but is possibly derived from Plectranthus ambiguous. Popular shrubby Plectranthus 'Mona Lavender' (ht 60-80 cm) also has dark-purple undersides to its leaves, complementing its pretty violet flowers.
In autumn I bought an interesting ginger relative known colloquially as bamboo ginger - Alpinia luteocarpa 'Red Rubin' - with green and purple foliage; however, it is not looking too happy with our current winter temperatures. I am hoping it is deciduous!
I'd be interested to hear of other plants like these that I could grow in my Sydney garden!
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