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Thalictrum — meadow rue

A penchant for meadow rues

Just about all gardeners have a hobby plant type or two - a genus or family they particularly like, for which they seek out as many varieties as they can get their hands on. In serious cases, this turns into plant collectorship and the obsessive compulsive tendencies that go along with that. I'm not sure I qualify for the worst category, but as hobby genuses go, thalictrum is certainly one of mine. I've tried to grow many, and have succeeded at a few. This page showcases the varieties that grow in our garden, and tells a little about my experiences with growing meadow rues.

I'm starting this page as November draws to a close, so I've no opportunity to run out and check appearances, or take a few extra photos - all that will have to wait till next year. For now, I'll draw on photos already in my collection, and my (not-so-photographic) memory.

The genus

Thalictrum is a genus of about two hundred herbaceous perennial species, widely distributed around the world (North and South America, Europe, central and east Asia, and Africa). They belong to the large buttercup family (ranunculaceae), also home to other garden staples such as clematis, columbines, anemones, delphiniums, and hellebores. Botanists distinguish them from other closely related genuses by their flower characteristics: the lack of nectar and petals, the way they bear seeds in achenes. They also note that some species are dioecious (male and female reproductive organs on separate plants), while others are hermaphrodite (boy and girl parts on the same plant). The latter tend to have the showier flowers.

Cultivation

I can't speak from a position of authority here - just report my own experience. In general, I consider thalictrum to be somewhat finnicky plants, worthy of good garden conditions - until they prove otherwise. By "good garden conditions", I mean soil with some good organic content, a position that's within reach of the sprinklers that I put to use when drought strikes, and some afternoon shade.

In our first attempt at growing meadow rue, we planted Thalictrum aquilegiifolium in a full-sun area that had otherwise good garden conditions. It lasted a year. In subsequent attempts, we've been sure to provide a bit of shelter from afternoon sun. On the other hand, the taller species in our garden (T. flavum glaucum, T. pubescens) get full sun, and are perfectly happy. In fact, these have a tendency to reach and flop when they get more than a touch of shade, so full sun is best. Similarly, T. rochebrunianum thrives in full sun, and I suspect many of the tiny alpines do as well.

The water requirement is probably less flexible - but since I've not dared plant them in areas that get very dry, I've no proof of this.

Propagation

Nearly all of my experience propagating meadow rues is by seed - most species grow upright from a small base, that doesn't appear to lend itself to division. An exception is T. flavum glaucum, which forms robust clumps that can be divided every few years. But let's focus on seed.

Germination results from my various attempts are detailed on the individual plant portraits. My experience of course reflects the species native to temperature climates. For these, generally, germination appears to require, or at least benefit from, a cold moist stratification period. In some cases, an initial warm conditioning stage may also be helpful. A few species sprout easily when sown at room temperature.

Only two thalictrum species have self-seeded in our garden: T. pubescens (abundantly), and T. rochebrunianum (sparingly). As you might imagine, collecting seed from these is easy. Although not a self-seeder for us, T. aquilegiifolium also sets plenty of viable seed. Others are much less generous with their seed production: T. flavum glaucum produces few viable seeds among many duds, while T. delavayi flowers less abundantly, and makes just a small number of viable seeds any year.

Leaf shapes and growth habit

The signature garden species is certainly Thalictrum aquilegiifolium. Meadow rues are not often offered for sale around here, but when they are, it's usually this species, whose name translates to "columbine-leaved". And sure enough, the blue-green, compound leaves resemble those of columbines, their relatives in the buttercup family, to the point where one might confuse one for the other before the flower stalk goes up. Several other species of thalictrum share this leaf shape, but others are much more finely cut, and some, like T. lucidum, are altogether different in appearance.

Meadow rues come in a wide range of sizes, from diminutive alpines species to towering herbs. They also vary in their habit - some are strictly upright, producing a single stalk that shoots up to produce the flowers; others produce multiple flowering stems, often with a more lax habit. This means that meadow rues can fill a variety of roles in the garden, finding niches in rock gardens sunny and shady perennial borders, and wilder gardens like cottage gardens and wildflower meadows.

Flowers

The color of thalictrum flower clusters (which may be determined as much by the stamens as by the sepals, which are missing or drop quickly in many species), ranges from white to yellow to lavender-blue in our garden. In many cases, individual flowers are only apparent close-up: from typical viewing distance, the effect is produced by the cluster as a whole. Where flowers are so separate that they make an individual impression, they usually face downward, weighed down by the heavy reproductive parts. Flowers appear in mid-late spring.

The midsized blues

This group of meadow rues includes the family sedans of the genus – the most common and steady performers. Besides the T. aquilegiifolium mentioned previously, I include T. rochebrunianum and T. delavayi in this clan. Although they share similar flower color in lavender spectrum and a medium height (2-4 ft), there's enough to distinguish them from each other.

Just peachy for the semi-shaded border, T. aquilegiifolium grows two to three foot tall. Its overall habit is upright, but there are multiple leafy stems so that the overall impression is more mound-like than stalky. The leaves of course resemble those of columbines in color and general shape, although nobody would confuse the mature plant, even out of flower, for a columbine. The flowers are often described as pink or rose, but to my colorblind eye, there's more of a blue contribution than you'd guess from those descriptions.

Unique among the meadow rues in our garden is the seed shape produced by columbine meadow rue. While all thalictrum seed is encapsulated in a husk, this species has little sails around the seed, giving the seed clusters a cool appearance.

Another popular species is lavender mist meadow rue, T. rochebrunianum. This is a much more strongly upright plant, with just one or a few flowering stalks extending about four feet up from a low-growing rosette. The stalks have an attractive purple cast. Although from a distance the flowering plant looks like a haze of purple, when you step closer it's much easier to see the individual flowers, much less densely spaced. Although it produces seed just as abundantly as columbine meadow rue, the seeds are in smaller husks, not so obvious when the plants are done blooming.

The least common among my blue species is Yunnan meadow rue, T. delavayi. In many respects, it is similar to lavender mist, but it is more delicate: the leaves are more finely cut, the flowers more delicately spaced along the stalks. And the stalks themselves are laxer, with tendency to arch that is charming as long as it doesn't turn into a flop. They make less of a statement in the garden, but they're just right in a genteel ensemble of prima donna perennials. Much as I love this plant, I've not been able to propagate it effectively - the small number of flowers produce even fewer seeds. I've never noticed any self-seeding, and my attempts to grow from seed have been unsuccessful more often than not. So it's a good thing that my original plant has survived all this time!

Yellow puffballs

Continuing for the moment the classification by flower color, let's turn to the yellow ones. There are two of those in our garden, rather different in overall appearance.

Let's start with yellow meadow rue, T. flavum ssp. glaucum. From the photo you can see that the origin of the yellow color is not the presence of yellow sepals or petals, but rather the absence of such structures, and the abundance of fluffy yellow anthers, all clustered together in dense flowerheads.

Leaves are produced a good ways up the stems, which can reach as high as 6 foot - so the whole plant takes some space. Some gardeners complain that the plants are prone to flop. Indeed, the ones we once grew in a part of the garden that receives afternoon shade did get topheavy and leaned over, although they never quite flopped all the way. So we relocated those - but the other cluster, which receives full sun, has never had any problem. They are in our back yard island, which has decent but not great soil, and gets supplemental water in drought but is not the first in line for water services. Conclusion: give these sun but not too much TLC, and they'll reward you with sturdy upright growth.

As the subspecies name suggests, the leaves are bluish green. They again resemble columbine leaves, and are soft and without sheen.

That's where shining meadow rue, T. lucidum, really takes a departure from the rest of the bunch. The leaves are dark green, glossy, and narrow, no longer resembling columbine in any way. Quite attractive, and the plants appear to be strong and hardy. Flowers are much like those of T. flavum, perhaps in somewhat denser, well-defined puffs.

Tall white guys

Departing from the lavenders and yellows, we arrive in white territory. The species in our garden that fit here are less showy, probably better placed in a meadow or woodland garden. Since we have neither, they share space with the rest of the perennials on our plot.

The first one of this description I got my hands on was tall meadow rue, T. pubescens (a.k.a. T. polygamum), obtained at a local native plant sale. Indeed this is a tall species, growing at least six foot tall and strongly upright. Multiple stems rise up from the basal mound, and weave an airy see-through pattern (which makes it hard to do them justice in photographs). White flowers appear in clusters in early summer, adding to the effect, even though individually they're not much to look at (our original and largest plant is female, which produces the less showy flowers). Dainty as it may look, this species is not shy about seeding itself around. The seedlings are only a nuisance in my off-years, where that part of the garden receives less attention than it needs. I'm not sure how that comes to be, because this is one of the dioecious species, which requires male and female plants to reproduce - and we started with just one plant. Perhaps a botanist can set me straight on that.

A second larger white one is purple meadow rue, T. dasycarpum. I grew this one from seed, and it hasn't been in the garden long enough for me to know its ultimate habit, but so far it looks like it will be shorter than pubescens. The genus name comes from the pronounced purple coloration of the stems; I must admit I haven't noticed this on our plants, so I can't be sure of their identity - next year should bring more opportunities to observe. What is clear is that this plant is different from others in our garden - the male flowers keep some of their white sepals, to surround the stamens, whose white filaments and yellow anthers make for an interesting bicolor when you look up close. The species name, meaning "hairy-carpelled", refers to the seed structure. I should check that, too.

One that we tried more recently is western meadow rue, T. occidentale. Supposed to grow 3-4 ft tall, but our second-year plants didn't reach half that height. So far I'd call the flower color not so much pinkish white (as other descriptions say) as greenish white - but I've probably only seen female flowers so far. I hope to have a better update next year.

Itsy-bitsy ones

Let's switch gears and take a look at a few that you have to kneel down to see properly. My experience with these types is limited, but here goes.

Our first little one came from seed for T. minus. The seedlings grew very slowly, eventually reaching the size shown in the photo at left. The leaves are tiny and ferny, in a shade of grayish-green. I used to think I'd missed the flowers year after year, but upon reinspection of my photos, I think it's more likely that the flowers just weren't as showy as I expected; the fuzzy enlargement at right shows typical thalictrum flower structures, with the bicolor filaments and anthers.

Another tiny one goes by the name 'Afghanistan'. I bought a plant once (which didn't survive), and also grew a crop from traded seed. Internet research places this cultivar either in T. minus adiantifolium or in T. isopyroides. In any case, in habit they are quite similar to my original T. minus. I hope to have a photo next year.

Finally, we grew alpine meadow rue, T. alpinum, from seed a couple years ago. These are a bit larger than the two above - so that the cute tiny-dissected leaflets, while almost as dainty in close-up inspection, is more evident from typical viewing distance. The flowers, on the other hand, are almost completely nondescript, as far as I can tell.

Other species

Even if I ignore the species from warmer climes (whose attraction is great but futile), there are many left to explore in our garden. Among the more gardenworthy ones are T. uchiyamai, T. orientale, and T. diffusiflorum. This genus can keep me occupied for quite a few more years – which is fine by me.

Further reading

For botanical information and a collection of photos, visit The Thalictrum Website of the Oregon State University Herbarium.

List of species in our garden.


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Last modified: June 17, 2009
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