"Tough beauties"

Meet an interesting plant family.
Sunday, 21 February 2016     

Catharanthus roseus

This summer I have had success growing a pretty and tough-seeming annual sometimes called the Madagascar periwinkle (or vinca) Catharanthus roseus. It has simple, flat flowers usually white, purple or pink, and enjoys our hot, humid summers, not wilting even on the most challenging days. It has been around in Sydney gardens for a long time, often regarded as fairly common, but in line with my current philosophy to go more for undemanding plants, I plan to grow it again next year and to seek out other flower colours: I have seen a lovely deep purple one in the garden of a friend, and some are bicoloured with a distinct 'eye'. Another plant that has been around forever in Sydney gardens is 'chain of hearts' (Ceropegia linearis, pictured at the start of the next paragraph): I remember it growing in a hanging basket on the porch of my parents' house many decades ago, with amazingly long pendulous stems bearing mottled silvery-grey leaves that really are shaped like hearts. I have recently been given a plant, which I plan to grow in a hanging basket myself in a semi-shaded spot. And I've just discovered that the Madagascar periwinkle and the chain of hearts in fact belong to the same interesting plant family, the Apocynaceae.

The family Apocynaceae contains around 410 genera, most of which come from tropical and semi-tropical parts of the world, including Africa, South and Central America, and India. The flowers of the plants are in the main simple and flat, like my Madagascar periwinkle, but they are often large and brilliantly coloured; many have a fleshy texture to them. The foliage of the plants is in many cases lush and glossy. They range from trees down to annuals. And lots of these plants do really well in Sydney gardens without requiring much cosseting, adding an exotic look.

There are a number of climbing plants in the family, and the most familiar in Sydney is the star jasmine (Trachelospermum jasminoides), with its glossy leaves and deliciously scented white flowers in late spring. Perhaps it is all too ubiquitous these days, but this vine has the advantage of growing and blooming so very well in shady parts of the garden, and can also be used as an effective groundcover plant. A variegated version has white and pink-splashed foliage. Another vine for shade in the family is alluring Hoya, with its clustered waxy flowers that look almost unreal.

Other climbers in the family that do well in Sydney include Mandevilla sanderi (syn. Dipladenia sanderi cultivars, with flamboyant funnel-shaped flowers of pink, white or red, which bloom almost all year round and can be grown in a large pot; Stephanotis floribunda (now renamed Marsdenia floribunda!) with white fragrant bell-like flowers; and the giant Beaumontia grandiflora with its simply enormous white trumpets. There is a wonderful specimen of Beaumontia festooning the fence near the Friends' Nursery in the Royal Botanic Garden Sydney. Though needing some sun for good flowering, these vines prefer a little shelter during the hottest part of the day in summer.

The frangipani trees (Plumeria rubra) that adorn many old Sydney gardens also belong to the Apocynaceae family. There are so many gorgeous colour variations of these available these days and they are still in full bloom at the moment. On a smaller scale, shrubby Carissa macrocarpa (the Natal plum) is another example, and it is sporting its clear white flowers now. It is one of the toughest shrubs in my garden, growing at the top of my long battleaxe driveway in a dry position that is never watered. It forms a rounded evergreen mound, and is rather spiny, being said to make a good front hedge to deter burglars.

A small shrubby perennial that is sometimes seen in Sydney gardens is the stunning blue-flowered Oxypetalum coeruleum (syn. Tweedia coerulea). It seems to do best in the Hills area, with colder winters and less humidity in summer: in one garden I know, it has self-seeded gloriously. I have never had great luck with it as it tends to rot off in summer, but I am going to try it again in early spring with some seeds from the garden where it does so well, and treat it as an annual in a sunny dry spot.

Vinca major and Vinca minor are groundcovers from Europe that belong to the family. I have an uneasy relationship with these plants as they can have a tendency to take over; however, they are useful for a dry shady area where other plants won't easily grow, and the variegated version can look very effective under trees (as illustrated at left). The pretty blue (or less commonly pink, white or plum) flowers appear in spring.

Most members of the Apocynaceae family exude a milky sap when the stems are cut or injured. Indeed, the sap of some genera was used as a rubber substitute in World War II when supplies of natural rubber were cut off. In some cases, the sap is quite toxic, and was used on poison arrows in some cultures. The tough old shrub called oleander Nerium oleander is a well-known poisonous member of the family. Handle all these plants with care. Some Apocynaceae plants were used in traditional medicines, and today, Catharanthus roseus is showing promise as a source of a drug for treating cancer.

 Reader Comments

1/6  Margaret - 2122 (Zone:10 - Warm Temperate) Monday, 22 February 2016

The Apocynaceae family (thank you for providing the name) is a very interesting family. I have had success with some members - Vinca, Dipladenia, Stehpanotis, Beaumontia and varieties of Cerapegia. It is fascinating to learn of the relationship and uses of this plant family. Your research is much valued. Thanks so much, Margaret. You certainly have a number of specimens from the family in your garden! Deirdre

2/6  Anne - 2518 (Zone:10 - Warm Temperate) Monday, 22 February 2016

as Margaret says thanks for providing the family - how interesting - re Catharanthus roseus - for some obscure reason Mum called it Billygoat plant!! you can buy punnets of the different coloured ones & Bunnings often have them in their potted colour. Noticed it used in apartment gardens round Forster. Love the colour of Tweedia - I too have not had much joy with it. The addition of the Mandevilla/dipladenias has provided great colour for many months to our gardens - love them. Enjoy your week. I love the name of Billygoat plant! I will be looking out for the different coloured ones. Tweedia is certainly a challenge but I think if I regard it as an annual I may have more luck! Deirdre

3/6  Carolyn - 2125 (Zone:10 - Warm Temperate) Monday, 22 February 2016

I agree with your thoughts on the Vinca - Catharanthus Roseus. My daughter has been growing this plant in a very hot dry position and it does so well. Even though it dies when the weather cools, once the warm weather starts again, there are lots of new seedlings to plant up - it"s the plant that keeps on giving without being weedy. I dug up some of these seedlings for my own garden and they are also doing so well. A great tough little plant. I wish I had grown it sooner! Will be putting more of it in next summer. Deirdre

4/6  Glennis - 2122 (Zone:10 - Warm Temperate) Monday, 22 February 2016

I have the Tweedia growing well in Eastwood. The plant was given to me about 15 years ago and it just keeps self seeding, in an area close to the main plant, without becoming invasive. A couple of times I have thought I have lost it and then it reappears. A very pretty blue. How wonderful, Glennis, to be able to grow the elusive Tweedia so successfully! I am determined to try it again. Deirdre

5/6  Robin - 2045 (Zone:10 - Warm Temperate) Monday, 22 February 2016

I have killed a tweedia at least once after falling hard for that pale summer sky blue. I know of no other flower with that particular tone, but I have had get over that broken love affair. It hates the humidity at my place. Thanks for the research on this handy family Deidre. Yes the Tweedia colour is unique. I do think it hates humidity; the garden where I saw it doing so brilliantly is in Glenorie, where lots of other humidity-haters were doing really well. I am going to give it one more go, though! Deirdre

6/6  Georgie - 2099 (Zone:10 - Warm Temperate) Monday, 22 February 2016

I have had Vinca self-seeding for years in the back garden: recently transplanting the wayward seedlings to other parts of the estate. They look great mass planted as a border plant along the easterly driveway, for instance. I have potted others and have them on the northerly steps leading to the front door. Tough as nails, once established they are drought tolerant, almost thriving on neglect, rewarding the gardener with months of cheerful flowers! Sounds like they are fab in your garden; I will definitely make more use of them in future. Deirdre

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