Robert W. Freckmann Herbarium

 Great White Lettuce (Prenanthes crepidinia) Population & Flowering 

Mark Mittelstadt property Iowa County

1988 thru 2003 (2004 updates)

I have found very little information regarding this species in Wisconsin (not surprising with only 3-4 known locations in the state).  I offer these observations and comments as a guide in management of the species, until someone finds time for a more rigorous study of the matter.

The site is a sedge meadow along the Pecatonica River.  The specific locations are very dense with large plants (cupplant, green-headed coneflower, etc).  The 1830s survey records suggest that this sedge meadow was treeless.

1998: When the plants were first noticed in late September, only the last flower was still open.  It was more yellow than the cream color described for the species.  A single plant was found near the ditch at the north end of the wetland, east of a large willow tree.  Two or more were found near the southeast corner of the wetland, along one of the fencelines, in two locations about 8 feet from each other.  (Note that basal leaves are gone by September, so any non-flowering plants would not have been seen.)

The remaining flower and several stem leaves were collected and pressed.  One voucher was sent to University of Wisconsin Platteville, one to Wisconsin Dept. of Natural Resources –Bureau of Endangered Resources. Since then I've been waiting for it to flower again.

Tree cover: Because this is described as a species of wooded floodplains, shade might be of some importance.  The SE location had a small box elder tree nearby that died a year or two before.  The N location has a small elm tree just east of the plant.  Neither was large enough to lend hardly any shade to the plants, and certainly had not large enough 5-10 years earlier to shade anything.

1999-2002 No further flowering occurred (and I checked carefully).  Basal leaves were found at one of the SE locations each year; apparently 15-20 plants packed close together.  No basal leaves or anything were found after 1998 at the other SE location or the N location.

Several dozen seeds had been collected in October 1998, which were sent to 2 nurseries.  One got several plants to grow, then planted them out in their wetland and hasn’t seen them since.  The other got seed lots confused and doesn't know what happened to the P. crepidinia.  We have been fairly certain of species ID, but as of 2002 have not been able to manage a flower for absolute confirmation.

The density of the plants at the one location is noteworthy.  I wonder if the species produces vegetatively.  If not, then either: a) There must have been a lot of seed dropped in this one spot from some earlier year's production, or b) This spot of a few square feet must be just the right habitat for the species, versus lots of similar looking soil a surrounding it.  Although I suspect vegetative reproduction, I haven't wanted to confirm by digging up the only location left.

As flowering was unsuccessful for several years, I thought about creating partial shade such as the plants may be adapted to in a partially wooded floodplain.  Snow fence or shade cloth suspended over the plants at 6-8 feet might work.  As of 2003, I haven't gotten around to trying this yet.

2003 Basal leaves appeared again at the one SE location.  I weeded lightly to give them a little more sunlight.  (The competition gets very heavy as the season progresses.)  I had weeded around them in the same manner in one or two of the prior years, but did not get flowering, so the extra sunlight by itself does not seem enough to do the trick.

On a field trip 16June with several other botanists, we located two plants bolting, about 2 feet tall.  For several years there had been only basal leaves.  I broke down the tops of adjacent plants to give a little more light to the top leaves and flowers.

20June:  Stems about 2.5 feet tall, larger stem leaves than before.  The flower heads were just beginning to appear.

22 Aug:  Flowering was just starting, stems 5-6 feet tall.
 West plant:  218* flowers, 18 already open or spent
  East plant:  156* flowers, 12 already open or spent
(* some very small flower buds were not included)

3 flower samples were collected & pressed, and several pictures taken. Basal leaves were entirely gone and some of the lower stem leaves were already brown. I broke down a few flower stems that were taller and overtopping the P.crepidinia, but left most of the lateral shade. 

1Sept: Both plants in full flower (1/2- of flowers open, 1/4 spent, 1/4+ not opened yet).  The weather is dry and apparently will be for most/all of the pollination period.  (I got several good pictures & a couple specimens.)  There has been a lot of deer activity around the area of the plants, but no feeding on them yet.  (At the same time, the nearby turtleheads are in full flower creating a nice display this year.)

Whatever seed I gather this year will be raised to seedlings for replanting.  If I do not find indication before outplanting, of what the correct habitat is, I intend to try a variety of wetness/shade combinations to see what works best.  My understanding is that it may be a species of flood plains with sparse tree cover.  If anyone has thoughts on this, I'd appreciate suggestions.

6Sept Bob Wernerehl, ecologist/botanist, observed that most of the flowers are spent and some of the first seeds are nearly ready.  (This has been a very dry year, which could affect timing of flowers even though the plant is in a wetland.)

15 Sept. The last 5-10 flowers are still open. The east plant has 192 flowers.  The West plan has 317.  Many of the small buds that previously looked questionable seem to have flowered successfully, very few failed.  Seed is not nearly ready; seeds of the first few flowers are still quite green.  The one opened had about 15 seeds.  Prime time for seed collection may be October 1-15? One of the stems had fallen, apparently from lack of lateral support.  Too many nearby plants had been knocked down during observation and pictures, and there was recently two days of continual rain.  The stem was not broken; it was propped up on other plants and should still produce seed.

22 Sept. I revisited the site to collect seed. Almost half of the P.crepidinia seed has been eaten by some larva. The larva seems fairly large to have grown from the seed in a single flower, and I wonder if they move from one flower to the other. The seed doesn't seem ripe yet, and I'm torn between collecting prematurely before its all eaten, or waiting until its ripe and hoping that there is still some left. And I was worried about the deer...?

Recognizing the Plant

I have found that recognition of this species can be challenging for us amateurs, even a little so for the pros.  The basal leaves are fairly distinctively Prenanthes, although they can be confused with blue lettuce.  They senesce by mid-summer and decay rapidly.  Flowering plants still have basal leaves when the stems start to grow, but have no sign of the basal leaves when the flowers begin to bloom.  The lower stem leaves also drop off as flowering occurs.  Non-flowering plants have no above-ground portions left beyond mid-July or so.

The stem leaves on flowering plants are nothing like the basal leaves, and the lower stem leaves are different than those on the upper stem.  Lower stem leaves tend to be triangular, more or less, similar to P. alba leaves.  Upper stem leaves are closer to the shape of elm or cherry leaves, sometimes with a larger tooth toward the base.

When the flowers are mature, they droop in a fashion typical of Prenanthes.  But when the flowers are still young, they can be mostly upright.  The bracts of the flower heads are distinctly hairy and there are from 20-25 florets in each head.

In July and August, plants without basal leaves and with flowers buds still upright may be difficult to recognize.  At this time, mine were 2-3 feet tall and in the middle of a taller dense wetland community.  At the end of August and through September, the 6 foot high stalk and drooping flowers are rather distinctive.  There is nothing else in my site, or anything else that I know of, which will look similar in September.

2004 Updates

June 14: We have 11 flower stalks coming up this year. This is from the same group of plants that produced the 2 stalks last year, and no flowers for several years prior. I found what seems to be two groups of P.crep on an upland site 1/4 mile away. They don't look like blue lettuce or P.alba, the two spp I sometimes confuse with P.crep. Further, the basal leaves are senescing in June, typical of the P.crep elsewhere.

June 22: They continue to look just like P.crep and I'm fairly convinced that they are. The leaves are senescing now, at the same time as other P.crep plants. The leaves look very different than blue lettuce and P.alba at this time, and I don't know of other species which would look similar.

This population is on a hillside, gentle N slope with fairly dense tree cover. (It's a different site than I've been told P.crep is found in, but I'm finding too many rare plants on the "wrong" sites to let this concern me.) The population consists of 3 groups of plants, only yards apart, with at least a dozen plant in each. The plants within each group are so close that they could have grown vegetatively. I have not found stray individual plants outside of these 3 groups to suggest regeneration from seed. The understory was cut in 2002(?) as part of the restoration project. I don't know if any leaves were evident before then. None of the plants have made any effort to produce flowers (and the ones bolting in the wetland are at least 3' high by now).

Some of the leaves were browsed, about 10-12" high. It looks like our deer like the taste, suggesting that they just haven't found the ones in the wetland.

I'm struck by how quickly the leaves decompose after senescing. Some that were in good shape or just starting to yellow on the 13th are completely gone. A few have the distal half of the yellowed leaf still laying on the ground, while the petiole of that leaf is already disintegrated.


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