Stern's Medlar, Revisited

Way back in the Dark Ages of the Fruit Blog, back when I actually wrote long articles, I wrote an post on medlars, which mentioned Stern's medlar, aka Mespilus canescens. I've always been fond of Stern's medlar, mostly because I'm fond of outliers in general, and this thing is definitely an outlier.

The genus Mespilus has long been one of those single species genera, consisting only of M. germanica, the European medlar. So the discovery in 1970 of a medlar species, a hemisphere away from all other naturally occuring medlars, in Arkansas of all places, is certainly surprising. The fact that it exists only on one site, with only 25 individuals, that it only rarely flowers, and that it turns out to be triploid, are that much more unusual.

In fact, probably too unusual to be the real deal. A little while ago I had a great e-mail from Thomas Frothingham, who has worked with M. canescens, with an update on the latest thinking on the species. I'll repost it here verbatim, rather than just paraphrasing his whole letter for you:

I happened across your website today, and I thought I would pass along some information about the Stern's medlar. In a former job, I worked extensively with this species in situ, at the Konecny Grove Natural Area. There has always been controversy about the taxonomy of this very rare plant, but the latest thinking, based on the genetic analysis of the entire Crataegus tribe by Dr. J.B. Phipps [EFL: The paper is actually by Lo et al., not Phipps, though Phipps has been a prolific researcher in the field of Crataegus and Mespilus taxonomy], is this: the Stern's medlar is an accidental hybrid between The blueberry hawthorn (C. brachyacantha) and the European medlar, Mespilus germanica. I can send you the original article if you're interested. It seems likely to me that the germanica plants were brought to the area early in the 20th century, when there was an influx of immigrants from the area of the Czech/Austrian border region. The influence of these settlers is very evident today: the nearest community is the town of Slovak, there is an Eastern Orthodox church nearby, the nearest cemetery is named the Czech National Cemetery, etc. Also the area is still populated with people of Czech ancestry (the Konecnys, Orliceks, etc).

At one time the population of Stern's medlar was managed as one of the rarest tree species in the world. If the hybrid theory is correct, it may change that perception. On the other hand, the blueberry hawthorn is tracked as a species of concern, and has been extirpated from the Grand Prairie region of east Arkansas (the original prairie has been almost entirely converted to rice production). So the Stern's medlar is at least preserving some of the genetics of a rare species.

To answer some of the questions posted on your blog:

To my knowledge, the Stern's medlar is not available commercially. Any attempt to market it would have to take into account the ownership rights of the landowners (the Konecny Grove Natural Area is privately owned, managed through a conservation easement by a state agency. It is also not open to the public). The plant also has some limitations as an ornamental: the period of bloom is very short, and the flowers smell bad. It has so far proven impossible to propagate by cuttings or tissue culture, although I assume it could be grafted. The only reliable method so far is to carefully dig up the suckers from around the base of the parent plant. There are some specimens at the Center for Plant Conservation in Missouri, and also I believe at the National Center for Germplasm Research in Corvallis, Oregon.

The reason it hasn't bloomed in recent years is probably due to the succession process, as the canopy closes and the plants are increasingly shaded. The use of prescribed fire and removal of surrounding trees has been implemented to reverse this process. The other problem with managing this plant in the wild has been the presence of invasive Japanese honeysuckle and privet. These plants have been removed manually, which is very labor intensive. The last time I saw it, the grove was in good shape. This natural area is also the habitat for a number of other rare plants, and so it will continue to be managed carefully, regardless of the conservation status of the Stern's medlar.

It would be extremely interesting to replicate the original cross between the two presumed parent species-in other words, cross pollinate between a European medlar and the blueberry hawthorn. The seedlings from such a cross would presumably be Stern's medlars.

He also passed along a copy of the Lo et al. paper* (which I would be happy to share with any one interested). It's not the easiest reading, at least from my point of view (as much as I like taxonomy I find taxonomy papers mind-numbing), but buried in there are the evidences for a hybrid origin of M. canescens:

1. Nuclear sequence data showed M. canescens shared a recent common ancestor with the M. germanica samples, but chloroplast sequence was actually much more closely related to C. brachyacantha.


2. Stern's medlar shares many characteristics with C. brachyacantha that it does not with M. germanica: petals that turn orange upon drying, multiflorous inflorescences.


3. C. brachycantha occurs naturally in Louisiana, eastern Texas, and adjacent portions of Oklahoma and Arkansas. M. germanica, while native to Europe, is recorded to have been grown in Louisiana as long ago as 1893, placing the two species in close proximity of the only known site of Stern's medlar.


4. Both sexual (×Crataemespilus) and graft (+Crataegomespilus) hybrids between Crataegus and Mespilus. (I've discussed the general promiscuity of the whole Mespilus / Crataegus / Sorbus / Pyrus / Amelanchier club before).


5. There are a lot of reasons to reconsider Mespilus' standing as a distinct genus and include it in Crataegus.

They basically propose the following scenario for the origin of M. canescens:

• Sometime, probably 150-200 years ago, pollen from cultivated medlars was transferred to a flower of blueberry hawthorn, resulting in hybrid seed.


• The resulting seed produced hybrid individuals. However, because of differences between the parent species, meiosis was irregular and the hybrids were largely infertile.


• The only viable gametes produced by this primary hybrid would have been unreduced, and thus diploid.


• With these unreduced ova, occasional seed set might have occurred, and in those cases the pollen parent could have been either a medlar or another native diploid hawthorn (possibly red-fruited, like M. canescens).


• Stern's medlar is the result of these secondary hybridizations.

I have to admit they lay out a pretty compelling case, both for revoking species status for M. canescens (they suggest designating it Crataegus ×canescens) and for absorbing Mespilus into Crataegus. But my personal taxonomic system is based more on sentiment than on anything else, and I'm definitely a splitter, not a lumper. So I'm going to keep Mespilus, and I'm going to keep calling Stern's medlar a medlar, because it's cooler that way.

*Lo, E.Y.Y., Stefanovic, S., and Dickinson, T.A. (2007) Molecular reappraisal of relationships between Crataegus and Mespilus (Rosaceae, Pyreae)—Two genera or one? Systematic Botany 32(3) 596-616.

The "haw-medlar", aka ×Crataemespilus grandiflora

I don't know how I missed this when it was posted almost a year ago. It's a spontaneous hybrid between a medlar and a hawthorn.

Haw-medlar identified in Worcestershire (Joan Morgan's Fruit Forum)

So do you blet this thing?

I've actually seen "Crataegomespilus" more than "Crataemespilus". The Great Arbiter, Google, shows a few more hits for the former, but a fair amount of both.

(I'm very disappointed in the spell-checker in this Flock editor—It flags both "medlar" and "blet" as misspellings.)

Update: Nevermind...I figured it out:

×Crataemespilus = true hybrid of Crataegus and Mespilus
+Crategomespilus = graft hybrid chimera of Crataegus and Mespilus

Graft hybrids are cool.

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Sure, it tastes lousy now, but try it when it's a little rotten!

Sometimes it's pretty obvious why certain fruits fail to catch on. Take the medlar, for example. A tree fruit which shares a family (Rosaceae) with such mainstays of American fruit consumption as apples and pears, and native to the eastern Mediterranean, it seems as though it would have been quickly adopted in Europe and shipped along to the New World with all the various other things, good and bad, to become part of our culture heritage here.

Medlars, however, are not exactly wildly popular in Europe, and most folks in the United States have never heard of them. That's because of their one big catch: they're basically inedible fresh. Off the tree even when dead ripe, they are hard, green, and extremely astringent. There are other fruits with this issue, and in most cases the problem is solved by simply making them into jellies or preserves, but even that (alone, anyway) does not work for the medlar. The solution to this is "bletting": ripe medlars are taken from the tree and spread on some rather absorptive material (like straw, sawdust, or bran) somewhere rather cool, and allowed to decay for several weeks. Ideally, they're harvested from the tree immediately following a hard frost, which jumpstarts the bletting process by breaking down cell walls and speeding decay. Once the process is complete, the flesh will have broken down to the point where it can be spooned out of the skin. The sticky mush substance tastes a bit like something somewhere in between dates and a weird, dry applesauce, with maybe a hint of cinnamon. I'm told its an acquired taste, but I've yet to acquire it (not that I've tried very hard to). I've been warned that there is a fine line to be observed here, and that letting medlars blet too long is a good recipe for an upset stomach.

As is the case with so many things these days, most folks don't really want to be bothered with that anymore. The medlar enjoyed a run of popularity during the Middle Ages and Renaissance, particularly in Tudor England, and Charlemagne specifically ordered them to be planted on his royal (imperial?) estates. Part of their charm in those days was that because they were harvested late in the season and then allowed to blet for many weeks, medlars were some of the very few sweet things available to eat in Europe during the winter. They enjoyed another run of popularity in the Victorian era as desserts, but with the advent of controlled atmosphere storage and worldwide food distribution, that particular reason to eat medlars is essentially gone unless you're a hardcore homesteader or live somewhere without a supermarket. They maintain a small niche today among gourmets, and in French cooking (which appears to have found a place for pretty much every edible substance on the face of the planet.)

Botanically, medlars are interesting in that unlike other related fruit, the seeds are born in open chambers on the calyx end of the fruit, a fact which prompted Chaucer and other writers of his era to refer to it as "the open-arse-fruit", and the French to nickname it "cul de chien", meaning "dog's asshole" (Other off-color medlar metaphors are no doubt the reason for the medlar reference in Romeo and Juliet...I believe there's another one in As You Like It, too). Such names probably don't do much for its popularity, and the fruit are, to my eye anyway, rather unattractive: a heavily russetted green, with a flared open calyx, rather similar to a deformed crabapple.

The tree, however, is more attractive than its fruit, with large, abundant, white flowers which would justify its use as an ornamental if not for the need to dispose of all the resulting medlars somehow (it is self-fertile, so even a single tree will set fruit). I've seen it described as a large shrub, but it always seemed more tree-like to me, especially since it can hit heights of more than thirty feet (though it rarely does, as it is rather slow growing). The leaves are dense, downy, and dark (how alliterative!). Quince or hawthorn are frequently used as rootstocks.

There a handful of medlar cultivars around, some of which are carried by nurseries. 'Macrocarpa' (meaning "big fruit") is among the most common, and is available in the U.S. from Raintree Nursery among other places. Honestly, this is the only cultivar I can recall seeing for sale in the U.S. (Edible Landscaping has a medlar for sale, too, but doesn't list the cultivar). Also popular (if a medlar can be said to be so) is the 'Medlar of Nottingham', commonly known as 'Nottingham', and 'Large Dutch' which are available from a variety of sources in the U.K. and Australia. Keepers Nursery in England has perhaps the largest selection of medlar cultivars I've seen. I'm not sure how international my audience is here, but while I'm on such a track I might as well mention that they're also available at Perry's Fruit & Nut Nursery and Daley's Fruit Tree Nursery in Australia and at Diack's Nurseries in New Zealand.

For quite a while, the European Medlar, Mespilus germanica, was considered to be alone in its genus. All that changed, however, when in 1990 a new species called Stern's Medlar was described in Arkansas. The new species, designated Mespilus canescens, is confined to a single population of about 25 individuals in the Konecny Grove Natural Area (there have been unconfirmed reports of individual trees outside this area). The new species has been suggested to be polyploid and may in fact be of hybrid origin, but the limited amount of material and the rather small field of medlar researchers have so far limited the amount of work done on the subject. Interestingly, although Stern's Medlar is known to have fruited in the past, none have done so for several years, despite prolific flowering.

Note that so-called "Japanese Medlars" are actually Loquats, Eriobotrya japonica, another Rosaceous tree fruit (I've been meaning to do a write-up on these for a while).

I'll end this entry with a question I've had for a long time: can anyone think of anything else one blets besides medlars? Some one once suggested persimmons to me, but I don't know that I've ever heard it used in that context. I find it strangely appealing that a fruit as obscure as medlars has verb dedicated specifically to it.

Sorbus: Genus of Easy Virtue

I've been poking around for a while, looking things up here and there on the topic of intergeneric crosses. One thing you learn quickly when you start paying attention to plant breeding is that the rules you learned in high school biology about what will reproduce with what go straight out the window. Crosses between species, supposedly not possible, are pretty much the bread and butter of most breeding efforts (to be fair, the real textbook definition of species was 'reproductive isolation', which doesn't mean they can't reproduce, just that they probably won't for whatever reason...but I'm not betting your eighth grade science teacher knew or expressed the difference). That restriction sort of gets bumped up to the next level. In general, you can't make crosses between genera.

In general.

Species and genera are, of course, made by Man, not Nature, and Nature seems to have this thing about finding exceptions to the rules Man has tried to come up with. Intergeneric crosses do work, sometimes. In my yard right now, I have a little plant that looks quite a bit like a strawberry, called 'Lipstick'. Unlike strawberries, however, 'Lipstick' has bright pink flowers. Really quite attractive, though I haven't had fruit yet to attest to it's worth in that respect. It's a cross between Fragaria x ananassa, the cultivated strawberry, and Potentilla palustris, a related species for sure but not a member of the same genus.

Fragaria and Potentilla are both members of the Rosaceae, a family of plants which contains maybe a majority of the fruit crops out there (and yes, as you may have guessed, roses, too). A number of the genera out there are willing to play a little fast and loose with the rules. In addition to Potentilla, strawberries have been crossed with Duchesnea indica, the "false strawberry", and with raspberries. Luther Burbank, perhaps the greatest American fruit breeder (though not a scientist by any means) was perhaps the first to make this cross, which resulted in some rather odd plants.

Burbank was one of the great makers of wide crosses. He crossed apples with pears, apples with rose, pears with quinces, strawberries with dewberries, etc. The Russians were also big on this sort of thing. Partly because their climate is almost universally horrible (I said "almost"...yes I realize parts of it are just lovely), Eastern Bloc breeders have always seemed a little more anxious than most to make weird crosses. One genus that seemed particularly amenable to their fiddling was Sorbus, or mountain ash.

Probably one of the better known intergeneric crosses in the family is 'Shipova', a cross of mountain ash and pear from Yugoslavia. It's available commercially here and there, and is actually pretty good from what I've heard. Russian breeder Ivan Michurin created 'Ivan's Belle', a hybrid between mountain ash and hawthorn, also available here. Hybrids of Sorbus exist with Cotoneaster, Aronia, Mespilus (medlar), and Amelanchier (serviceberry), and it's tempting to wonder how many other obscure ones might work if some one tried them enough. Some of the hybrids, like Sorbaronia have been found occurring naturally!

Ultimately, though, the successes of intergeneric crossing have been few and far between, though its promise to any breeder is obvious: opening up an entire new pool of germplasm. If only it was that easy.