Exciting houseplant deliveries don’t always come in large boxes; I am equally thrilled by padded envelopes containing clear plastic bags. That’s how my collection of Smithiantha started, in the form of several small, scaly rhizomes sent through the post. These rhizomes may alarm the uninitiated due to their resemblance to the kind of grub you might find nestled under a rotting log, but they get better.
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Smithiantha is my favourite genus of the gesneriad clan, and not just because it is one of the relatively few to be named after a woman in horticulture: Matilda Smith, born 1854, an illustrator who became botanical artist in residence at the Royal Botanic Gardens, Kew. They are native to southern Mexico, and known for their Penstemon-like flowers and exquisitely plushy red and green leaves. I started out with a cultivar called ‘Extra Sassy’, bred by US hybridiser Dale Martens, with coral-red flowers and a spotty yellow throat. The warnings in the few references I could find on Smithiantha informed me that these plants are tricky, requiring high humidity, warmth and strong light, my plant clearly hadn’t read the rules, because it bloomed and looked glorious. Soon I was stalking about on eBay, buying more rhizomes of other cultivars: they too blossomed.
After flowering, the plants start to flop and fuss in winter, and that’s my cue to let them dry out completely, storing the pots somewhere out of the way. Once spring is under way, I tip out the pots to remove the rhizomes, and repot in fresh compost. I’m told this is one of the reasons the plant isn’t more popular – people like their houseplants to look the same, all year round. How dull. With smithianthas, you get to reboot your plants every year, and there is nothing more thrilling than watching those unpromising rhizomes burst into life.
Gesneriads are classified as flowering houseplants: they all have flowers that are fused into a tube shape, and are zygomorphic – meaning they display mirror symmetry. Yet their foliage is often just as striking. You will probably already be aware of African violets (Saintpaulia), Cape primroses (Streptocarpus), or perhaps, the florist gloxinia (Sinningia speciosa). The genus Primulina includes many cultivars with equally striking foliage and flowers, while Petrocosmea are compact enough for the tiniest of windowsills or shelves. Florist gloxinias and other members of the Sinningia genus grow from tubers, and there are many dinky Sinningia cultivars, such as ‘Tinkerbells’, that have a passionate following among gesneriad enthusiasts.
How to grow gesneriad houseplants
When considering how to care for gesneriads, it’s hard to generalise for a range of genera that come from every continent barring Antarctica, but a few simple principles will help you start out. Midday sun will burn the leaves, so don’t stick them alongside your cactus collection. My plants do very well in a north-facing kitchen windowsill with a skylight above. The hairy leaves will be damaged by any wet splashes, so water from below by placing plants in the sink and letting them soak up what they need, but only do this when the soil has dried out on the surface. Self-watering pots can also work well. Occasionally dust the foliage with a clean soft paintbrush, and turn pots regularly to make sure the plants grow evenly. Before long, visitors will be begging you for a cutting of these underrated plants.
How to propagate gesneriads
Most gesneriads can be propagated from a single leaf: just remove a leaf – petiole and all – and trim the petiole with a diagonal cut. In the case of the larger-leaved species such as Streptocarpus and Primulina, a section of leaf cut with a clean, sharp blade will work just as well. Insert the leaf petioles or cut leaf sections into damp cutting compost and cover with clear plastic: before long, baby plants will begin to grow at the base. In the case of smithianthas and other gesneriads that produce scaly rhizomes, such as Kohleria and Achimenes, it is even simpler: just tease out a rhizome and pot up on its own in spring.