Cryptanthus (‘Earth Stars’)
Cryptanthus is a genus of flowering plants in the family Bromeliaceae (Bromeliads), subfamily Bromelioideae. The name is derived from the Greek word cryptos, which means hidden, & anthos, meaning flower.
Cryptanthus species are predominantly native to eastern Brazil, in coastal areas as well as in forests up to 2000 metres. Some grow well in humid, shady places & others grow in dry, bright locations, but only a few species will tolerate full sunlight.
There are currently 56 species listed on the Bromeliad Taxon List & over 1200 cultivars listed on the Bromeliad Cultivar Register.
Photo right: Cryptanthus ‘Marion Oppenheimer’
These attractive, colourful bromeliads have a shapely rosette made up of leaves with serrated, wavy edges. The accumulation of trichomes in silvery shades creates an amazing pattern on the reddish-brown or green leaf surface which gives the species & hybrids an interesting & vivid appearance. Most have low spreading rosettes with about 10-12 leaves which are often mottled & striped with many unusual colours such as brown, rose, silver, copper, grey, green, pink, white & red or a combination of these colours. The flowers, which barely emerge from the centre of the plant, are usually white, rarely pink or greenish.
Species in this genus often grow spread out over the ground like small ‘earth stars’ which is often how they are referred to by bromeliad enthusiasts.
In their natural habitat Cryptanthus are true terrestrials (growing in the ground) & a few are saxicolous (growing among rocks). They have never been observed as epiphytes (living in trees) & should not be mounted on wood or in trees. They need to be planted in pots or in the ground.
Photo right: Cryptanthus acaulis Variegated
When potted, they should not be under-potted. Their roots tends to grow sideways rather than downwards & thus develop a root system at least equal to the width of the mature plant. So a 130 to 160mm squat pot is suggested for most Cryptanthus to promote root growth & to conserve the moisture the plant requires. The smaller varieties can be potted in smaller pots that equate to their mature width.
The potting medium should be a loose, porous mixture with some humus similar to African Violet mix to replicate the rich moist soil in which they usually grow. Some options are an African Violet mix, a good quality potting mix or a mixture of peat & sand & perlite.
If planted in the ground, the soil need to be free draining.
Cryptanthus should not be allowed to dry out. Leaf die back can indicate lack of water. However, lack of adequate drainage in the potting medium or soil can cause the plant to rot.
Although it is not necessary to fertilise your Cryptanthus, you must do so to obtain maximum growth & colour.
A controlled release granular fertiliser combined into the potting mix shows excellent results. Use one that is recommended for African Violets or Orchids (higher in potassium K than nitrogen N). All fertilisers will show the N:P:K ratio.
Soluble fertilisers can also be used instead of or combined with controlled release fertilizers. Use dilute solutions, even to ¼ of the recommended strength. I also use a higher potassium than nitrogen soluble fertiliser (as for flowering plants / orchids / African violets) but there are others who recommend a balanced nitrogen & potassium fertiliser.
There are Cryptanthus that will grow in any light conditions you may have. C. beuckeri is a low light plant & many of its hybrids (e.g. C. ‘Osyanus’) like to be shaded, moist & humid (this makes them ideal for terrariums). Species such as C. bahianus & the hybrid C. ‘Cascade’ can take full sun, but the plants are happier in diffused light.
For maximum colour in most Cryptanthus, bright, filtered light is necessary. Too much light will cause bleached spots on the foliage or a leathery, stressed look to the plant. In extreme cases, sunburn spots or holes will occur. On the other extreme, weak foliage & greening of colour suggests that the plant needs more light.
Acclimatise your plants to grow in as much light as possible in the area you have set aside for them, a spot that is sheltered from the cold & winter rains would be desirable. This may be a shadehouse, outside with filtered light or in a window garden. Fluorescent light intensifies colour – this makes them an excellent office plant.
Cryptanthus are comfortable in temperatures that human beings prefer i.e. 15 – 28 degrees C.
Most Cryptanthus can survive in temperatures just above freezing as long as they are kept drier during winter, but they will not look their best. Some can even survive winter outside if a heavy mulch is used & watering is cut back in Autumn to allow the plants to harden off. Severe leaf damage may result but the mulch protects the roots & Spring brings on abundant offsets.
At the other extreme, they can tolerate temperatures as high as 38 degrees C as long as there is adequate humidity, good air circulation & the mix is not allowed to dry out.
Cryptanthus are easy to grow outside in temperate regions where there are no frosts or cold winter temperatures & make exotic garden plants. They seem to do well when grown outside in QLD & similar latitudes, but in Sydney & regions further south, they need protection from the cold & winter rains.
Most Cryptanthus enjoy humid conditions both inside & outside the home. This can be achieved by frequent misting, setting the pots over water or grouping together. Setting the pots over water with capillary matting does a great deal to increase humidity & maintain moisture.
Cryptanthus will grow in well-lit bathrooms or above the kitchen sink where the humidity is usually greater.
Insects & Disease
Cryptanthus are relatively pest free. If you encounter scale, use a systemic insecticide following all the safety precautions & do not use in high temperatures. There are various natural treatments which can be accessed online.
As with most bromeliads, the parent plant only blooms once in a lifetime & dies after producing offsets (pups). Although the name Cryptanthus means hidden flower, you are rewarded at maturity with a bouquet of delicate flowers. Different species & hybrids flower at different times of the year.
Your Cryptanthus will produce offsets before or immediately after blooming. These normally come from between the leaves, from woody stolons or from the base of the plant.
Offsets may be left on the mother plant for multiple growth or may be removed when ready (about 1/3 the size of the mother plant) with a slight twist & tug. The pup will release easily when it is ready.
Some plants release their own offsets when they are sufficiently mature.
Don’t be alarmed that there are no roots on the offset. In nature the offset will roll to a new location or will take root in the decaying humus of the mother plant thus forming clumps or mats.
Your plant will root easily in your potting medium. Make a small depression, insert the short stem & press the mixture around it (easier if the medium is wet). Stake the plant if necessary to keep it from moving. An elastic band is also useful (of the appropriate size) for holding the offset in the mix. It is essential that the plant feels secure for an extra fast start & good growth.