Undulata variations, or Where are my stripes?
Photo essay by David Teager
I'm not an Undulata. Slugs don't like me!
Back in the early days of Hostas on the Internets, a nice man named Henk Hooijer created a web page showing the known variations of the Undulata group of hostas. Henk has recently passed away (2016), and that web page had long passed into the realms of the internet archive (a.k.a. the Wayback Machine), but you can see it, with some broken links, here. This is my attempt to recreate the information, with additional commentary.
In early research on the genus Hosta, Undulata was considered a species (Bailey, 1923) based on exported specimens, with three key types known: white centered ("mediopicta"), white edged ("albomarginata") and all green ("erromena"). Later research shows that these plants are all related, but none of them (notably the all green one) is found in the wild. George Schmid rightly demoted them to cultivar status in 1991. This means that they are considered a hybrid of garden origin, with no determination of its hybrid origins. At some point, genetic analysis may solve the riddle. In this way (and perhaps there is a genetic relationship as well), it bears resemblance to the Fortunei group, also a related set of plants of unknown, ancient, hybrid origin.
The members of the Undulata group, not surprisingly, show strong similarities. Each will have leaves of thin substance (slug food), with about eight vein pairs on each leaf (don't count the middle vein). They all have broad petioles with rippling edges, which helps distinguish them from other hostas. They bloom at about the same time, and with the same long bloom scapes and pale lavender flowers that I don't hesitate to deride as "wimpy." In fact, if there were ever a good argument for cutting hosta scapes before they bloom, Undulata is it. Also notable is that Undulata, with very rare exception, never sets pods with viable seed. (I think there are only two seedling offspring known.)
So, without further ado, here is the handy guide to the Undulata group.
White-centered: 'Undulata', 'Undulata Univittata', and special selections
Hosta 'Undulata', where the white center is more than 1/2 the leaf width.
'Undulata Univittata', where the white center is less than 1/3 the leaf width.
'Undulata Univittata' losing its variegation, with 'Undulata Erromena' forming.
The white-centered forms of Undulata can be undeniably attractive in springtime, where they emerge with bright colors. However, this plant is so often abused by planting in challenging locations (too much sun/heat), that by mid-summer it is a tattered mess with a misty green haze overlaying the center variegation. Then, over years, it can too easily follow the pathway toward losing the variegation entirely, resulting in an all-green plant that will quickly outgrow any variegated remnants. Growers in other climates may have more success in keeping it looking good, but here in the mid-Atlantic, this set of hostas cannot be highly recommended.
Which is not to say that many people won't grow it. Because it grows prolifically (whatever the variegation pattern), it is the #1 starter hosta, as gardeners are always happy to unload a big bag of divisions.
When attempting to identify an unknown white-centered hosta, Undulata should always be the first choice, no matter how many people want to think they have the much choicer 'White Christmas', 'Night Before Christmas', or 'Fire and Ice' cultivars. Those are, in fact, members of the Fortunei group, and can be distinguised from Undulata on a number of points. They are much more garden-worthy, if you want the white-centered look, especially 'Night Before Christmas'. Other, newer hostas, might be even better at giving this look, but none will self-multiply to the point that you can line a walkway with it.
'Undulata Univittata' with late summer green "uglies."
You'll see in the photo captions above that I left some wiggle room in distinguishing between 'Undulata' and 'Undulata Univitta'. As discussed above, this is something of a moving target. If you have a good 'Undulata' and wish to keep it that way, the answer is to divide it, perhaps every two years, and replant the newly "young" clump.
In addition to 'Undulata' and 'Undulata Univittata', there have, over time, been selected white-centered forms registered with the international registrar. You may find 'Kiwi Spearmint' and 'Middle Ridge' (or 'White Ray'), which are selections (although not stable long-term) of 'Undulata' and 'Undulata Univittata', respectively. You can find these at the Hosta Library. Do note that "Hosta mediopicta" and "Hosta variegata" (and the like) are not valid registered names for Undulata forms, despite what some growers will put on the tags.
White edged: 'Undulata Albomarginata'
Bloom close-up on Univittata for comparison: they're the same.
This one is pretty self-explanatory: the Undulata with a white edge. As shown in the pictures here, the leaves can be broad or slightly narrow, perhaps a variation in growing conditions or a true variation within the cultivar. The leaf edges should be slightly rippling. And of course the flowers have the same wimpy presentation.
It is notable that mutations of 'Undulata Albomarginata' are extremely rare. And it truly grows like a weed, so you can, in a matter of years, divide and redivide a single big clump to line out a 10-meter border. Just keep the slugs away, and don't neglect water. It really doesn't want to be in full sun, either.
All green: 'Undulata Erromena'
While "erromena" means "vigorous growth," it might also have something to do with "error." The good is gone, and you're left with a fast-growing green hosta, quickly eaten by slugs, and with blooms that beg to be removed before they appear. Yes, I am strongly biased. There are way too many good hostas (even green ones) to keep this hosta. You may have a sentimental attachment that makes you biased the other way.
There may be rare mutations of 'Erromena', such as the white-edged (and unattractive) 'See Saw'. Henk Hoojier listed an 'Undulata Kifukurin' that would have a gold edge, but I've only seen pictures of a single specimen (shown as a sport, not as a named plant).
At the very extreme, there are sports of 'Undulata' that actually come up without any green at all! These are 'White Feather' (from 'Undulata') and 'White Trouble' (from 'Undulata Albomarginata'). Each will turn green a few weeks after emerging, if you are lucky enough to keep them alive. (Note that in 2016, a number of third-rate mail-order nurseries seem to be selling 'White Feather'. Beware! You probably won't get a good plant.)