Wednesday, July 28, 2010

Wildflower Wednesday: Bedstraw & Curdled Milk - Updated

As a follow-up to last week’s Fireweed and its horn-tailed muncher, the misnamed Bedstraw Hawk Moth, I thought that this week I’d feature the ignored host: bedstraw (Galium spp.). While Alberta is adorned by several perennial wildflowers in the genus, Galium is probably better known in its weedy annual incarnation: Cleavers (Galium aparine). Cleavers (aka Sticky Willy) is especially pernicious in canola fields because its seed is of similar size to rapeseed and the plants clinging hairs stick to the canola stems and interfere with harvest*.
 Other introduced perennial galia are somewhat weedy, including the attractive yellow-flowered bedstraw G. verum (once used to curdle milk for making cheese – hence Galium from the Greek gala for milk), but one species is usually a welcome addition to a garden: Sweet Woodruff (G. odoratum). Fellow Edmonton garden-blogger The Far North Garden had a good posting on Sweet Woodruff a few weeks ago. She’s having far better luck than I in growing it: in the Home Bug Garden it is just barely hardy – surviving the winter under snow, but loosing out to the freeze-thaw springs.

When it thrives Woodruff makes an attractive ground cover in shady spots. The white flowers are fragrant and the vegetation gives off a pleasant smell when crushed. Coumarins are responsible for the smell, variously described as ‘new-mown hay’, ‘vanilla’, and ‘nauseatingly cloying’** - the latter being how some people react to its use in flavouring German May Wine. Both smelling nice and repelling bugs were the reasons mattresses used to be stuffed with bestraws. Unfortunately, coumarin is a liver poison and a vitamin-K inhibitor, so perhaps the enjoyment of Sweet Woodruff should be limited to smelling, and tasting avoided.
 The crushed leaves of Northern Bedstraw (Galium boreale – sun to shade, Zone 2) have a bit of a new-mown hay smell to them, and were used in mattresses in the Old World (the species is circumpolar), but have smooth stems that do not cling. The tops of the plant are covered with white flowers for several weeks in June and July. My patch is planted in a rather unsightly spot in deep shade and I find it quite attractive in an understated way. I suppose the seeds would get stuck in your socks, but my plant does not set seed – probably because it consists of one self-incompatible clone – so it seems to have no drawbacks and is just tall enough to pop-up at the back of its bed.
 Beetles and small flies are reported as the pollinators of Northern Bedstraw and among the small flies are mosquitoes, some of which are reported to find the flowers highly attractive (Chang 1966, Plant Protection Bulletin of Taiwan 8:50-63). Although acceptable forage to cattle and an important seasonal food source for Prong-horned Antelope (Jacques et al. 2006 Prairie Naturalist Volume: 38: 239-250), levels of insect herbivory to the leaves seems to be fairly low (Agrawal & Kotanen 2003 Ecology Letters 6: 712–715; Agrawal et al. 2005. Ecology 86: 2979-2989). The herbivorous arthropods that I have been able to find records for are all borers and gall formers, e.g. the agromyzid fly Praspedomyza galiivora – described by KA Spencer from nearby Whitemud Creek (Mem. ent. Soc. Can. 64: 1-311, 1969), a couple of gall mites (Phyllocoptes calvus, P. anthobius Liro 1941 Ann Zool Soc Zool Bot Fennicae Vanamo 8: 1-54), and the maggots of the gall midge Ametrodilopsis auripes that forms nodules on the roots of Northern Bedstraw (Tikk & Sil'Vere 1982 Eesti NSV Teaduste Akadeemia Toimetised Bioloogia 31: 150-161).
 Most species of Galium considered native in Alberta have whorls of 4 ‘leaves’ (actually 2 leaves and 2 leaf-like stipules), while the introduced species have whorls of 6-8 leaves. The exception is Sweet-scented or Fragrant Bedstraw (G. triflorum) that has leaves in whorls of 5-6. I haven’t yet seen this forest understory plant in the field, but it looks like it might make a more hardy replacement for Sweet Woodruff as a ground cover for shady spots, although its small greenish to white flowers are much less impressive.

UPDATE - I spent some time watching patches of Galium boreale in flower in the bush this weekend to see what kinds of insects visit the flowers. Visiting flowers isn't the same as pollinating, but it gives a useful first approximation. Over about 20 minutes of checking a half dozen small patches with the close-focussing binoculars I saw mostly tumbling flower beetles (Mordellidae) and small black ants, but also a yellow-faced bee (Hylaeus sp.), a small male ichneumonoid wasp, an even smaller chalcidoid wasp, and three flies (a picture-winged fly [Callopistromyia sp.], either a grass-fly coloured like Thaumatomyia or perhaps a similar-looking agromyzid leaf miner, and a male mosquito).  So, it seems a good variety of tiny insects find the flowers attractive.

*Royer, F & R Dickenson. 1999. Weeds of the Northern US and Canada. The University of Alberta Press. / Lone Pine.

**Small, E. 1997. Culinary herbs. NRC Research Press.


  1. I've seen that sweet little bedstraw plant along the edges of the paths of the ravine and as a volunteer in the back lanes. I had no idea it was related to Sweet Woodruf, which has been very successful for me in previous gardens. I will be adding some to this garden as well as it is a good spreader but not too agressive in our zone.

  2. Our Sweet Woodruff also spread quite well on the north side of our house, but there are always areas that die back over winter. So far there has always been enough survivors to repopulate the bed before winter hits again.

  3. Hi Garden Ms S & Zone 3b:

    I guess it is encouraging to know that everyone else has had more success growing Sweet Woodruff here in Zone 3. I'm down to 1 shoot after three years of decline. Maybe I'll try some more in a better spot.