Tuesday, 11 June 2019

Mongoose-leaf and Cliff Sausages

Plectranthus ernstii

One of the easiest houseplants I have grown. Covered in masses of flowers from May until December.  Leaves mildly aromatic, something like ginger and zonal pelargonium. I keep the plant dry from December to March. I feed with a liquid feed from March to August. I use a well-drained mix of two parts coir compost and one part perlite. It is important to avoid over-watering and waterlogged compost. I keep it on a west-facing windowsill.

The plant will tolerate quite severe underpotting but will need watering more regularly if there is almost no compost. The one above had been in a 7.5cm (3 inch) pot for several years but the pot was curving a lot for a square pot. I only potted it into a 13cm (5 inch) pot this year. Square pots are always best for plants, though they are a little more expensive.

Many growers take the name bonsai spurflower seriously and plant them in very shallow bowls. It is very slow-growing compared to many other Plectranthus which become huge very quickly. Perfect for the lazy or prevaricating houseplant fan. They should be potted up at the end of the dry season. Leave them for a few weeks before watering after potting-up.

I have had no success rooting cuttings the few times I tried. I should probably try again earlier in the year, before the flowers start.

Some of these flowers show little patches of damage. I think they are from an unsuccessful photoshoot a few days before. The light was not enough and I moved the plant around close up against a white tarpaulin.

Said to grow up to 25cm (10 inches) in the wild. Mine is 26cm at the highest leaf, 34cm including the flower spike. The flowers are 15mm high and the flower tube is 8mm from calyx to the point it splits.

There are said to be five cultivars (cultivated varieties) in horticulture. Unfortunately, I can only find enough descriptions of these to restrict identification of my plant to either Oribi (the original collection) or Foster's Foley collected from a place called Foster's Foley. The Oribi cultivar is said to be the best "bonsai" so I suspect that is the one I have.

One of the Afrikaans names for Plectranthus ernstii is kransworsies, translated as "cliff sausages".

First collected for botanists to identify from the Oribi Gorge in KwaZulu Natal in 1977 by Ernst Jacobus van Jaarsveld and his wife Erma. Named after Ernst by Leslie Codd when he first described the plant in 1982. Ernst collected more than 23,000 specimens of different plants during his career. Ernst has also written over 100 botanical articles and many books for scientists, succulent lovers and the general public. He wrote The Southern African Plectranthus and the Art of Turning Shade to Glade, illustrated by Vicki Thomas and published in 2006.

Ernst Jacobus van Jaarsveld
Picture from Librarything

The plant was found in pockets of soil in rock crevices and steep south-facing cliffs. The stems were described as "thickened at the base, up to 20mm or more in diameter, becoming brown and potato-like with age." This characteristic is said to be unique to Plectranthus ernstii, though some other species are stem succulents or have thickened bases. Though first only found in Oribi Gorge the plant has been seen as far south as the Msikaba River, about 80km (50 miles) from the Oribi Gorge. The wild plant is classified as "Near Threatened" with fewer than 10 known locations.

My plant was labelled as Plectranthus ernestii, which seems to be a common spelling error online.

The plants in the wild experience a rainfall average of 800 to 1500mm per year. Manchester in the UK has been quoted as 810, 867 and 929mm of rainfall per year. Obviously, we don't have a dry season in Manchester.

Every new shoot produces a spike of flowers.

Plectranthus zuluensis

This plant is one of the Plectranthus that is a bit too vigorous for a houseplant unless you like re-potting frequently. It is also very floppy and tends to rest on the surrounding plants or on the window. It might become more compact with more light but does not seem to suffer from the light levels it gets from an east-facing window. The last time I re-potted it I had to prune it to about 10cm (4 inches) above the soil. That was partly to unwind it from the surrounding plants and partly because it was just falling apart when moved.

I could not get a photo of the whole plant because it is so embedded into the surrounding foliage. Because I could not move it away from the window I had to put a padded envelope behind the flower spike to diffuse the sunlight.

First described for botanists by Theodore Cooke in 1909. The herbarium specimen had been received at Kew in 1865. They had been sent by the Liverpudlian plant collector William Tyrer Gerrard. He died of fever in Madagascar in the following year at the age of 34. The natural range of the plant is much larger than that of Plectranthus ernstii but it is also found in Oribi Gorge. It occurs "from the northern parts of the Eastern Cape through the coastal region of KwaZulu-Natal to southern Swaziland [Eswatini]". In many places it is common.

The variety Plectranthus zuluensis "Lupatana" is said to have pale flowers like mine and reaches about 80cm. The true species has darker flowers from deep purple-blue to pale blue-mauve and is said to get to 200cm in height. Mine is 75cm at the highest leaf. Mine might be Lupatana, but there are other cultivars available. I have it in a 20cm (8 inch) square pot. I got it in September 2017 as a very healthy little plant in a tiny pot, from Shrubland Park Nurseries.

The flowers are 18mm high and the flower tube is 14mm from calyx to the point it splits. The bulge at the bottom of the flower tube is 5mm tall. The leaves are mildly aromatic, a little gingery and lemon pelargonium (geranium).

I have not tried taking cuttings yet because one is quite enough for me, for the moment.

I am disappointed that my plant is probably not the wonderfully-named "Devil's Knuckles" variety. Though it is the right size, that one has purple flowers.

The name is wrong

Plectranthus have been called spurflowers. The name was composed from the Ancient Greek πλῆκτρον (plektron) and ἄνθος (anthos - meaning flower) in Ancient Greek.

Plektron had several meanings:
a plectrum (such as those for strumming on a lyre)
a spearpoint
a cockspur
a rudder
a goad for driving animals
a tongue (perhaps a sharp tongue?)

Unusually, the person who made up the name of the genus recorded their reasoning. Charles Louis L'Héritier de Brutelle made it clear in his Stirpes novae of 1784 by using the Latin phrase calcar gallinaceum (spur of a male chicken) to translate πλῆκτρον. The name came from a nectary spur behind the flower, an extension of the flower tube behind the calyx. Unfortunately, it seems that the first species he described, Plectranthus fruticosus, was the only one to actually have a spur.  The other 324 accepted species (according to The Plant List) are named for a character they do not have.
This may be disturbing to the botanists and gardeners who have a desire for neatness. However, the rules are to preserve the earliest correct described genus and species for the name of the plant, whether the name of that genus is appropriate or not. There are many plants that have a different colour than their botanical name would suggest or even come from different countries. Capsicum annuum, the species that has both sweet peppers and hot chili, is only an annual in those places where the cold kills it in winter.

Perhaps we should translate one of the Afrikaans names for common use. Spoorsalie means track-sage. Muishondblaar means mongoose-leaf due to the strong smell of the leaves.

It is a shame that there is still one species left accepted as Solenostemon, which used to contain a lot of plants now known as Plectranthus. We could have translated that from the Greek as groove-threads.

I have had a hard time finding Zulu names for Plectranthus. There is uJikwe and uJilo for Plectranthus esculentus. That has edible tubers so that might be like calling them all potatoes.

Plectranthus species I have grown and loved but never photographed

I grew Plectranthus rotundifolius from tubers that I found being sold in an Indian grocery, Worldwide Foods at 24 Slade Lane, Longsight, Manchester M13 0QE (no website). They originated in West Africa where the Europeans called them Hausa potatoes. They have many local African names, the Hausa call them tumuku. They have several names in India as well, including Kannada: ಸಂಬ್ರಾಲಿ sambrali, Konkani: कूक kook, Malayalam: koorka, koorkka, Tamil: சிறு கிழங்கு siru kizhangu. The tubers were very tasty and I got a few tubers produced by the plants. They grew very enthusiastically during summer. The leaves are quite thick and succulent. I lost them over winter, possibly because the plant got damaged by being underpotted in an unheated room and it suffered a rot that turned the whole plant into slime. Several other species are cultivated for their tasty and nutritious tubers, including Plectranthus edulis and Plectranthus esculentus.

I have grown several aromatic Plectranthus from dry areas, with succulent, velvet-covered leaves.

Plectranthus socotranus is from the seriously dry little island of Socotra in the Arabian Sea. I bought a healthy little plant from a British Cactus and Succulent Society sale for £1 odd. The poor plant never thrived under my care and soon lost its roots and slowly shrivelled.

I had far more success with three similar species I bought from Abbey Brook Cactus Nursery. Their online list is badly formatted. One was sold as Coleus aromaticus (now called Plectranthus amboinicus), which it clearly was not as the leaves were much smaller and furrier and the plant was very much smaller. Another was sold as Coleus aff. pentheri, meaning it looks a bit like Coleus pentheri but had not been properly identified. The third was sold as Plectranthus spec. CB189. They were all very clearly species of Plectranthus. "Coleus aromaticus" has a minty/herby smell. "Coleus aff. pentheri" has a smell very reminiscent of Vick's Vaporub. Plectranthus spec. CB189 had very neat leaves in four rows up the stem and a smoky smell. They were all very easy to grow and cuttings rooted very quickly. Eventually I lost interest in them, as I never got them to flower and the smells were not my favourite. I would recommend them for anyone who wants a cute, velvety silver succulent that will tolerate being forgotten regularly and is very easy to propagate. Kept dry in winter, from December to March. If you have lots of light and warmth they might not need to be kept dormant in winter. Watering for the rest of the year and light feeding in spring will give you a rapidly-growing plant that will provide plenty of rooted cuttings to give away to friends.

I grew Plectranthus prostratus from seed from Mesa Garden, though it seems they don't sell it now. It grew easily and quickly and produced a thick ground cover with tiny leaves. It soon flowered continuously, though the flowers were so tiny that it was very difficult to see them. The leaves did not seem to be aromatic at all so I gave up on it when I ran out of room.

I once had a Plectranthus verticillatus  - a well known trailing houseplant with waxy, shiny succulent leaves. Weirdly called Swedish Ivy though it is native all along the Eastern edge of South Africa from the Cape Province northwards to Eswatini (Swaziland as was) and Mozambique. It was too prolific for the small space I had at the time and I gave it away.

I also grew quite a few specimens from Chiltern Seeds' Plectranthus Mixed Species seed.  Several were nicely aromatic but all were too large and shrubby for houseplants. They were a lot bigger than I was expecting and that winter I tested their frost-tolerance in the garden. None were winter-hardy in Manchester.  All died. They also had the only pest I have had on my Plectranthus plants - the mint psyllid. It was not terribly destructive. I was mostly just intrigued by such an unusual and specialist insect.

The best-known of the genus is Plectranthus scutellarioides,  still known as the "Coleus" though botanists changed the name in 1975. Botanists have placed the coleus in at least seven different genera. They are well-known houseplants grown for their spectacular, strongly-coloured leaves with markings in shades of white, red, orange, yellow, green, brown and purple. I have grown a few over the years, always easy and fast-growing.

I had not realised quite how many Plectranthus I had grown over the years until I made this recap. If I had more room I would grow many more, they are very rewarding plants.