Family: Iridaceae

When one looks at the basic level of organisation required for landing, bees and aeroplanes have a certain amount in common. Whilst there seems to be no place for semaphores in the natural world, a wide array of flowers (including irises) have evolved markings with similarities to airport runways – for the purpose of guiding their pollinators to the desired destination.

In most cases, the reward at the end of these floral landing strips is nectar, with pollen an inevitable (and valuable) byproduct of all that fumbling around in a confined space. This is termed a ‘nutritive’ reward, for obvious reasons.

However, one fascinating (and mesmerisingly beautiful) group of irises has gone down a very different evolutionary pathway for attracting its pollinators. The Oncocyclus irises1 (also known as aril irises) produce no nectar and comparatively little pollen. Intriguingly, the non-nutritive reward that they offer is the provision of overnight shelter, primarily for solitary male bees from the tribe Eucerini.

And that’s pretty much it; the pollination of an entire section of irises effected by a bunch of furry loners looking for somewhere to spend the desert nights. By all accounts, there isn’t even any romance going on in these ad hoc bachelor pads. Given that long-horned bees (as eucerine bees are commonly known) nest in the ground2, it is unsurprising that Oncocyclus irises take on such enigmatic mineral tones – as demonstrated by Iris atrofusca below.

Iris is a large genus (of around 300 species) that occurs in a wide array of environments across most of the Northern Hemisphere. Its relatives in the Southern Hemisphere belong to a range of related genera (within the family Iridaceae), including our native Libertia species.

Our interest is primarily in Iris species (as opposed to cultivars); especially those that integrate sensitively with planting schemes in which the structural planting is based on native ecology. In such associations, the flowers of species such as Iris pallida, I. filifolia or I. chrysographes can perform a role as emergent seasonal highlights amidst rolling shrublands, grassland or fern meadows.

Iris filifolia

Whilst retrospect is not an ideal lens for viewing life, it is useful for providing renewed focus when we return to places. And with this thought in mind, if I do go back to Gibraltar, I’ll direct my attention towards seeking out this classically beautiful iris species on the limestone cliffs and outcrops of the Rock of Gibraltar (rather than delinquent apes or the largest Dracaena that I have ever seen3).

I was introduced to Iris filifolia¬†several years ago by the excellent nursery, Hokonui Alpines, and we still grow the same stock purchased from Pete and Lou Salmond. Our other plants were grown from seed from stock originally collected in mountains to the west of Malaga by Oron Peri. Aside from its simple elegance and intense flower colour, this species’ resilience is a significant attribute weighing in its favour.

Although it naturally occurs within dry, relatively open habitats4, it has demonstrated a tolerance towards competition and varying moisture levels within our experimental garden (and projects in which we have planted it). In common with several other Spanish bulbs, Iris filifolia‘s distribution extends across the narrow gap to Morocco.

Iris graminea

Plum-scented iris

The habitat photos included within this plant profile (of Iris graminea in the wild in Croatia) are provided by Logan Drummond. As with all other images on the O2 Landscapes website, ownership resides with the photographer, and these images may not be used or reproduced without the consent of both Logan and O2 Landscapes.

One of the unintended benefits of spending time with other plantspeople (whether in wild populations or gardens) is the spontaneous sharing of knowledge. This can relate to the discovery of hitherto-unknown species, but it also opens up opportunities to ignite or revive interest in plants that one already knows.

One such conversation spurred me on to trial Iris graminea, on the basis of a friend’s comments about the strong plum/vanilla scent that this species’ attractive flowers produce. Scent is one of the most visceral qualities that one can include within plantings (with its connection to memory), and is therefore frequently discussed during our design process.

The upright foliage of I. graminea generally reaches 20 to 30cm in height, and charts a more graceful course towards dormancy than many larger Iris species (such as I. sibirica or I. setosa). When specified within plantings that emulate some of the qualities of the wild places in which it grows (such as the Croatian woodlands pictured below), its compact nature allows Iris graminea to take on a comparatively subtle role.

Iris graminea grows well within our warm northern climate, where we tend to position it with some degree of shade. Logan’s observations from visiting these natural populations were that it favoured lake margins and forested slopes where moisture collects, and that it is capable of tolerating significant amounts of shade (thriving within the leaf litter of these deciduous woodlands). The species has a very broad distribution, occurring from the mountains of northern Spain eastwards to Ukraine in a variety of habitats.


  1. Technically speaking, the aril irises are members of the Section Oncocyclus, within the Subgenus Iris. Amongst enthusiasts, they are often referred to simply as ‘Oncos’. And whilst we’re being pedantic, the aril irises (so named on the basis of their distinctive seed morphology) include members of Section Regelia (in addition to Oncocyclus).
  2. Similar to our native bees, which are also ground-nesting.
  3. The canopy of this tree appeared to cover an area equivalent to perhaps an eighth of an acre.
  4. Brian Mathew noted the description (by one Major-General M. W. Prynne) of typical habitat as “terra rossa crevices between limestone rocks”, within his book, ‘The Iris’ (1981. London : B. T. Batsford). Terra rossa is a particularly well-drained soil type associated with limestone and dolomite substrates in the Mediterranean.