Have you heard of urn heath (Melichrus urceolatus)? I hadn’t, until July last year. It grows along most of Australia’s east coast, but only in Box–Gum Grassy Woodland ecosystems (update: also in other ecosystems! see Greg Steenbeeke’s comment below). For most of the year, it’s an unassuming, prickly little shrub, usually less than 1 metre in height. Then in late winter, it bursts into a mass of tiny creamy-white urn-shaped blooms. Each individual flower is only a couple of mm in size. But a shrub in full bloom will stop you in your tracks.
This is what happened last July, as I took my regular afternoon walk through a local urban nature reserve. The reserve (Eastern Hill in Albury, NSW) is a tiny fragment of the Box-Gum Grassy Woodlands that were once common across the region.
This particular urn heath shrub was in full bloom right next to my walking track, but I’d never noticed it before. I didn’t recognise the botanical family, so I stopped to have a closer look, wondering if it was something special. And that’s how I discovered a couple of parasitic wasps supping on nectar inside the tiny urns. They are Diapriidae species, thanks to Ken Walker at Museum Victoria for ID.
Urn heath has no special conservation status, but that doesn’t mean it’s not interesting. The genus Melichrus is endemic to Australia, and includes only 5-7 species. Going by the published scientific literature, there isn’t a great deal known about Melichrus ecology. In particular, no one is quite sure how the flowers are pollinated, although bees are considered the most likely candidates.
Like many plants in fire-prone ecosystems, urn heath is a good post-fire resprouter. A couple of weeks after I spotted the plant in Albury, we went on a road trip holiday through New South Wales. One of the highlights was stopping for a walk in the Warrumbungles National Park, 2.5 years after the fierce bushfires that burned through 80 % of the park. I was excited to find the characteristic little shrub I associated with home blooming from the burnt ground in its northern NSW range!
Urn heath’s floral traits and phenology, along with knowledge of other species in the same Ericaceae sub-family (Styphelioideae), raise some intriguing questions on plant-pollinator relationships.
The flower’s colour (pale green–white) is thought to be almost invisible to bees; but its tubular shape implies animal pollination. The pollen structure (monad units) is mostly found in wind-pollinated plants; but a little appendage at the base of each anther suggests a trigger mechanism for depositing pollen on the backs of insect visitors. The plant blooms in late winter, when most bees and insect pollinators are not active, suggesting it doesn’t rely on insects for pollination; but it also produces copious amounts of nectar, which is a major attractant for animal pollinators.
Another example of why pollination syndromes are rarely realistic!
So what’s the story? Is urn heath insect-pollinated, like most of its relatives? Or does it have a more complicated reproductive strategy? Research is needed to answer these questions. But it’s clearly an interesting plant. In addition to its mysterious pollination ecology, it is obviously an important late winter food source for insects in Box-Gum Grassy Woodlands, at a time when not much else is in flower. Yet the potential for urn heath, and other winter-flowering plants in the Box-Gum woodlands, to support pollinator populations hasn’t been fully investigated.
My natural history note on this observation has just been published in volume 16 of Cunninghamia, one of Australia’s leading (but under-appreciated) natural history journals, focused on plant ecology. It’s open access, so click through to read the full article or download the pdf here.
Postscript: after the article had been accepted, I discovered the same plant in my local reserve had bloomed for a second time, in mid-summer. It burst into new buds just after Christmas, possibly in response to an unseasonal cold snap we had just experienced. Three months later, the buds are still there, unopened, frozen in time, teasing the local pollinators!
Do you know anything about the mysterious urn heath?
© Manu Saunders 2016