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Selaginella uncinata. Image © 天問小窩; retrieved from Wikipedia

Elaphoglossum metallicum, another iridescent plant. Image © In Situ Plants

Iridescent plants are a welcome addition to the interior landscape: who wouldn’t want a shimmering blue plant in their presence? There are several species (most only marginally available in cultivation) that exhibit this exciting type of colouration; Selaginella uncinata is perhaps the most available, under the name peacock spike moss. It can sometimes be found at garden centres and the like, and is produced by Exotic Angel Plants, amongst others.

I recently read an interesting article in The Scientist magazine on natural iridescence which explained something fascinating: iridescence is not caused by a pigment or a dye, but a structural property of the leaf (or wing, or feather, or whatever). Textures of the tissue surface are covered in ridges, bumps and dimples that refract the light in a way that appears to us as a metallic sheen. This adaptation is thought to have arisen during the Cambrian Explosion, as creatures were developing the first primitive eyes able to sense light, dark and contrast.

In cultivation, plants known for iridescence such as S. uncinata can show more or less of this colouration under different cultural conditions: I find that the best conditions for S. uncinata are moist, shady and humid (my default conditions for the genus). In bright light, this plant will blush pinkish-red, which can create a spectacular effect coupled with the iridescent blue, though it is a fine line to achieve both and maintain both colours. Apparently the ratio of red to far-red light makes a large difference in the production of iridescence, at least in the related species Selaginella willdenowii., though that`s somewhat outside the realm of the casual grower to play around with.

But perhaps the most intriguing aspect of this whole thing is the why: what evolutionary benefit do plants gain from this colouration? A paper published in the Journal of the Royal Society suggests two possible advantages: the iridescence may act as a deterrent to herbivores, as the (seemingly) constantly changing shape would not allow herbivorous insects, for example, to develop a search image (a familiar shape which the insect recognizes as a food source: search images abound, in our own minds as well as those of insects). The other possible advantage is that the iridescence (which is primarily seen in shade-dwelling plants, as I mentioned earlier) can prevent damage from exposure to too much light, say from a newly created hole in the canopy overhead that permits direct sunlight to reach the forest floor.

Whatever the reason, these plants hold a special fascination, and they are beautiful to behold. With a little care, these can make incredible additions to anyone’s indoor garden (and outdoor garden, if you are fortunate to live in a place with mild enough winters to get away with it).

Unknown Phalaenopsis hybrid. Photo © Arad; retrieved from Wikipedia

In Situ Plants interior landscapes, vertical gardens, and other plant installations in Toronto — Bulbophyllum 'Elizabeth Ann Buckleberry', probably one of the most commonly grown plants in the genus. Photo © Ed M.; retrieved from The Orchid Source

Did your eye even register the photo to the left? You can be forgiven if so: a beautiful sight it might be, but the now ubiquitous Phalaenopsis has become such a commonplace sight in homes and commercial settings that it’s nearly impossible now to regard them as the spectacular plants they are.

Tissue culture, offshore production and improved shipping techniques seem to have contributed most to the availability of these plants at nearly any place that sells plants (and quite a few that don’t): the US imported an estimated 400 40-foot containers of Phalaenopsis in 2010, and that number has surely risen since then. The plants are then forced into flower in greenhouses and then make their way to the mass market a few short weeks later. (This hasty method of production, though certainly bringing production [and thus retail] costs down, can also produce plants which may not perform as well after they leave the greenhouse, but that is a whole other post for another day.)

But why has Phalaenopsis become the poster child for the entire orchid family? After all, there are more than 26,000 species of orchid worldwide (many of them, admittedly, not suitable for culture, such as this exceptional species). Phalaenopsis was already being grown as a cut flower, which made it a good candidate for the early research into commercial production, and it is a very easy plant to grow commercially, growing rapidly and flowering reliably under the right conditions.

I don’t really have anything against Phalaenopsis in particular: there are over 60 species in the genus (check out the photos here), to say nothing of the countless hybrids therefrom. I’m definitely glad that more people are trying these plants out and having success with them. But it just seems a shame that the full diversity of orchids isn’t well represented in the mass market. The whole charm of orchids, after all, is their exoticness, and it certainly gets a lot more exotic than Phalaenopsis. Even other commercially produced genera offer a little more curiosity, and these are often easier of care for the novice than Phalaenopsis, and can also have more unique foliage so that they hold visual interest when not in flower.

It doesn’t seem as though the humble Phalaenopsis is going anywhere any time soon. Perhaps the best we can hope for is that other species become equally well-represented in commercial production. And my personal hope is that many species become so well-represented: the Orchidaceae really are incredible, and everyone should have the opportunity to try growing something a little different.

The world of plants is one of staggering variety: to date there are around 400,000 species known to science, with many more waiting to be discovered. An interesting facet to this variety is the fact that there can be incredible diversity within species themselves, such that different individuals of the same species growing side by side might not be immediately recognizable as being at all related.

Oftentimes, a variety will supercede the parent species in popularity, perhaps because it performs better in cultivation or has a more interesting appearance, and becomes used more often than the ‘original’ species. (Note that I am not discussing man-made hybrids or cultivars here- that is a subject for another time.) A perfect example is Dracaena fragrans ‘Massangeana’, which sports a pale green stripe down the center of its leaves not present in the typical D. fragrans. One doesn’t even really see the boring old D. fragrans anymore, so popular has its variegated variety become.

But would the effect of ‘Massangeana’ not be greater if it were a single specimen amongst several of the regular D. fragrans? After all, that’s how one would find such a variety in nature: they would stand out like a sore thumb, and perhaps even give taxonomists a run around thinking it might be a different species. I think it would, and so that’s what I do with these types of plants.

I believe that, rather than leaving these varieties to stand alone as representatives of their species, they should be incorporated and used (sparingly) with their parent species to highlight and exemplify the fact of their origins, and to allow people a glimpse at the near endless variety of the plant kingdom.

A. peruvianum gametophytes, in a somewhat underwhelming photo. Image © In Situ Plants.

Closeup of Adiantum peruvianum showing sori. Image © In Situ Plants.

I recently noticed, to my great excitement, that some fern spore had germinated in one of our vertical gardens. In this case the species in Adiantum peruvianum, the Peruvian maidenhair fern, a delightful species with unusually large pinnules (leaflets), and which eventually grows fronds a metre long in ideal conditions. When this species was planted, the fertile fronds were already showing the sori (clumps of sporangia which produce the spore) along the margins of the pinnules, and I had hoped (and had really thought it was against the odds) that some of the spore would in fact do its thing in the garden. Lo and behold, here we are.

You may know that the ferns are a fairly primitive group of plants that were on earth a million years before the dinosaurs, having only a rudimentary vascular system and never having developed flowers or seeds. In the right conditions, propagation by spore seems to be an extremely effective means of reproduction, provided a few basic needs are met.

In flowering plants, a seed produces a plant which grows to maturity, produces male, female or dioecious (male and female) flowers, pollinates and/or is pollinated, and the pollinated flower then produces seed to complete the cycle. In ferns and other spore-producing plants (mosses, liverworts and tree ferns), spore germinates and produces a gametophyte consisting of a single simple leaf called a prothallis. It is the gametophytes which do the reproducing in these plants: the male organs of the gametophytes release sperm, which, dependent upon the presence of a film of water on the surface of the growing area (certainly one of the reasons why these plants are usually restricted to moist, humid environments), travels between gametophytes and fertilizes the female organs. At this point a new plant is produced which is immediately more recognizable as a fern, and which will reach maturity and itself produce spore to complete the cycle. Colonies of gametophytes can apparently continue to produce ferns for some time, so in cultivation plantlets can be removed and the colony left to continue to reproduce, which is a pretty good deal.

With my little A. peruvianums, the first part of the cycle is complete (although perhaps it’s difficult to call a part of any cycle the first part). What remains to be seen is whether germination can be achieved: the outermost layer of the garden material does not have the constant film of water that the habitat of A. peruvianum does, but I am attempting to keep the area as moist as possible in an effort to assist germination. Here’s hoping for a favourable outcome; the little gametophytes certainly do add an interesting element to the garden, though, at any rate.

Immature Monstera dubia. Image © Anna Haigh; retrieved from CATE Araceae

Philodendron hederaceum and P. 'Brazil',growing as nature intended. Image © In Situ Plants.

We love plants for who they are. We like to see them grow as they have evolved to do, and vertical gardens provide a perfect medium for many plants to do so. The epiphytes (those plants that grow upon trees and other plants) and hemi-epiphytes (those that start life on the ground and then grow up towards the canopy) in particular are very at home in this environment, provided a few basic needs are met.

Without reaching too far into the reasons why many vertical gardening systems are designed to be densely planted from the outset (it seems to have been a natural progression for the industry to provide an instantaneously lush and full garden instead of one which required time to reach its intended glory), we can easily see the effects on the plants themselves. Commonly used plants which typically climb in their natural habitat are perfect examples of this: how often do we see a pothos or Philodendron climbing up a wall instead of cascading down? The weeping effect that the latter creates is admittedly pleasing (though there are plants which naturally possess this type of growth), but I believe that to create a truly spectacular and natural effect the best thing is to allow the plant to grow naturally; that is, up. And to do this, the plant needs space.

Many vertical garden systems are composed of cells, many filled with growing media, and some merely holding potted plants. These systems are fantastic if frequent replacement of plants is necessary, but this type of growing environment does not emulate a natural one. Other systems employ an undivided planting area, where roots are free to grow where they will. In these systems, if a plant is provided sufficient space, it will begin to grow upward, affixing itself to the growing surface with its aerial roots, tendrils, suckers or rhizoids, depending on the species in question. Once growth begins in this fashion it progresses rapidly, and something even more fascinating begins to happen: the plants’ new leaves begin to grow larger than the last! Simply as a result of being able to grow as it has evolved to do, the plant performs better and produces a nicer specimen than one constrained in a planter.

his effect becomes more dramatic still in the case of some hemi-/epiphytic species because they possess a juvenile and adult form. Monstera dubia is a splendid example: the juvenile form of the plant grows with its silver-brushed leaves tightly appressed to the growing surface, but when it reaches maturity it suddenly abandons this growth pattern to produce large green leaves which take full advantage of the higher light in the forest canopy. It uses this extra energy to finally, after its long climb, produce flowers and ultimately reproduce. Incredible!

Many designers of vertical gardening systems seem to have lost their way; in what other horticultural discipline has a garden ever been designed to be instantaneously lush and full (or crowded, for that matter)? Certainly not in most traditional landscaping, and not even in most interior landscaping situations. It is a pity that now many people showing an interest in these gardens are expecting such fullness at the outset, for it is truly at the expense of the true potential of the vertical garden and the species therein.

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Plants that Shine: Iridescence in the Indoor Garden

Why I Hate Orchids

On Natural Variation and its Place in Interior Landscaping

Ferns from Scratch, and Some Interesting Facts about their Method of Reproduction

The Space Between: Why the Immediate Lushness Effect Works Against Itself