Have you ever seen a truly green rose, with flowers as green as the leaves? I am not talking of that faux variety some people are talking about, but the genuine article.

I speak of Rosa chinensis ‘Viridiflora’, a flower of which is photographed below. A truly Green Rose!

Flower and bud detail of the Green Rose (Rosa chinensis ‘Viridiflora’).

I am not a rose enthusiast. In fact I consider that most cultivars make for quite unattractive shrubs if one ignores the blooms. When I used to work in a retail nursery, customers would frequently come to me and boast of their roses. But secretly, I could never get past the reality that for a month’s flowers in summer, one has to look at a thorny leafless twig in winter and often a sparse leggy shrub in the warmer months. Personally, there are other plants I favour more.

What I do enjoy growing are unusual plants that arouse genuine interest in people, because they are uncommon; ‘novelty’ plants if you like. And the Green Rose is certainly one of these!

I purchased mine from a grower many years ago. So long ago in fact, that I cannot even remember the person from whom I bought it. But I do recall I had to search a vast number of nurseries in and near Melbourne before I could locate one. Many rose ‘specialists’ had not even heard of this cultivar. The nursery which supplied mine had sold all, except one. That single specimen was in such a poor state that eventually the nurseryman was compelled by his conscience to give it to me for nothing. After a considerable amount of time, I was able to nurse it back to health.

Rosa chinensis ‘Viridiflora’ (also known incorrectly as Rosa chinensis var. viridiflora) was reportedly first observed some time before 1743 and introduced into culture by the British nursery firm Bembridge & Harrison in 1856. (I don’t know when it was introduced into Australia). The Green Rose will grow to a height of 1 metre and similar width. Like all cultivated roses, it needs to be cut back hard in winter and propagation is by cuttings grafted onto R. multiflora rootstocks. There is no perfume derived from this species, and that is because of the flowers.

Green is a little unusual, wouldn’t you say?

The ‘flowers’ of the green rose are barely that at all. In fact it is a genetic anomaly that is presumed to be the key to the Green Roses’ existence. There is an abnormal process that sometimes occurs in plants, called phyllody. Phyllody is where some or all of the organs from the four wholes of a flower (sepals, petals, androecium or gynoecium) are replaced with leaf-like (vegetative) organs.

The development of flowers is controlled by ‘floral organ identity genes’, most of which belong to a class known by plant scientists as the MADS-BOX gene family. These come in three flavours, ‘A’, ‘B’ and ‘C’. You can read about them here. In essence these three classes of genes are belived to control the development of the four whorls of flowers in what is described as the ‘ABC Model’. If one of these genes does not co-operate, perhaps because of a transcription error or mutation, then the flower – or all the flowers – will be mutated.

Scientists have demonstrated this with Arabidopsis thaliana (mustard) by removing various combinations of floral identity genes and examining what the resultant flowers look like. Fascinating stuff, but I digress:

The Green Rose is a ‘model’ of the failure of this system because all of the whorls are mutated except for one – the sepals.

Sepals are the first whorl in a flower; those leafy-looking bits where the stem joins the flower head. In the Green Rose, the ‘flower’ consists of the sepals and a ‘leafy’ middle. Basically the petals (corolla), androecium (male portion) and gynoecium (female portion) have become vegetative. The result? A green (albeit severely mutated) flower.

This is probably because the ‘B’ and ‘C’ floral organ identity genes that control the corolla, the gynoecium and androecium are either absent or mutated somehow in this cultivar. And this prevents the normal development of the flower by causing them to turn leafy.

So at the end of the day, we are left with this most unusual looking rose that arouses so much interest and is so highly sought.

Isn’t plant science interesting? There endeth the lesson!

Scientific references:
Coen, E.S. & Meyerowitz, E.M. (1991) The war of the whorls: Genetic interactions controlling flower development, Nature 353: 31-37
Chmelnitsky, I., Khayat, E. & Zieslin, N. (2003) Involvement of RAG, a rose homologue of AGAMOUS, in phyllody development of Rosa hybrida cv. Motrea. Plant Growth Regulation 39: 63-66