Lactuca biennis (Tall Blue Lettuce)

Plant Info
Also known as: Blue Wood Lettuce, Biennial Blue Lettuce
Genus:Lactuca
Family:Asteraceae (Aster)
Life cycle:annual, biennial
Origin:native
Habitat:part shade, shade; moist woods, thickets, swamps, stream banks
Bloom season:July - September
Plant height:2 to 7 feet
Wetland Indicator Status:GP: FAC MW: FAC NCNE: FAC
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 7+petals Cluster type: panicle

[photo of flowers] Branching clusters at the top of the plant and arising from upper leaf axils. Clusters are initially tightly packed and spread out as the plant matures. Flowers are ¼ to 3/8 inch across with 15 to 30 pale blue to whitish rays (petals). The bracts are variable in size, green often with purple tips, hairless, overlapping, appressed, and form a tube about ½ inch long.

Leaves and stem: Leaf attachment: alternate Leaf type: lobed Leaf type: simple

[photo of leaves] Leaves are rather variable. Those near the base of the plant are up to 12 inches long and 6 inches wide, deeply divided into several wide, coarsely toothed lobes with pointed tips, roughly triangular or arrow-head shaped in outline, with “winged” stalks. Leaves become smaller with fewer lobes as they ascend the stem; uppermost leaves are more lance-elliptic and may be stalkless and unlobed.

[photo of leaf underside] The upper surface is hairless, the lower typically has short sparse hairs along the veins, especially the midrib.

[photo of stem and winged leaf stalk] Stems are hairless to sparsely hairy, green, purple or purple streaked, and unbranched except in the flower clusters. Leaves, stems and roots exude a milky sap when broken.

Fruit: Fruit type: seed with plume

[photo of fruit] Flower heads form seed heads about 1-inch in diameter with the bracts spreading out as seed matures. Seed is brown, flattened, generally elliptic, with a tuft of light brown to grayish hairs to carry it off in the wind.

Notes:

Most similar is Wild Lettuce (Lactuca canadensis), which is distinguished by its typically yellow flowers, white hairs on the seeds, leaves that are often clasping and that have hairs only on the midrib. Some references split L. biennis into multiple varieties based on leaf shape, but these distinctions are not recognized in Minnesota.

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More photos

Photos by K. Chayka taken in Ramsey County. Other photos courtesy Peter M. Dziuk.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Maureen C - SE Winona County
on: 2009-08-30 07:01:17

This is growing in my flower border, Winona. I live very close to the Mississippi River, river mile 711.

Posted by: Meg - NE corner of Goodhue County
on: 2015-06-05 11:36:41

I had two plants show up in different flower beds on opposite sides of my house this year. I had never seen these before in the 20+ years we've been living there.

Posted by: Bruce - Minnetonka
on: 2015-07-14 11:52:46

I have at least one of these growing in a wooded area on my property. It hasn't bloomed yet and is at least 8 feet tall. It was hard to ID. It's leaning quite a bit so maybe it's longer to make up for the loss in height. I never knew lettuce could get this big.

Posted by: Pat - Wisconsin
on: 2015-07-19 15:26:30

I have one of these growing on the north side of my garage. I have never had one growing in my farmyard before, but it has been a wet summer. So I was glad for the link so I can identify this plant. The one growing outside my door is almost 8 feet tall, and just starting to blossom. I am in central WI. Just a comment to share.

Posted by: Mary Sue - Mahtomedi (East shore of White Bear Lake)
on: 2015-08-09 19:29:08

What a surprise--my first ever view of Tall Blue Lettuce. One grew up on the north side of my house in front of the kitchen window where I have a very good view of it. I would guess it is 10-12 ft. tall, and the top 2 1/2 feet have about 30 stems laden with tiny daisy-like flowers. All the "lettuce" is below that.

Posted by: suzannah - driftless area, Wisconsin
on: 2016-07-22 19:07:55

I had two growing by my back door until strong winds felled them both last night. they were 18-20 feet tall! the stalks about 1.5 inches in diameter. I've never seen anything like them.

Posted by: Jay r - Austin
on: 2017-06-05 19:34:46

I collect the white sap to make sleep potion

Posted by: John F - near Lutsen
on: 2017-08-09 11:59:28

I would like to plant some of these. Where can seed be acquired to put in before this winter.

Posted by: K. Chayka
on: 2017-08-09 17:10:24

John, we do not track who sells what. Please try "where to buy native seeds and plants" that is shown on most pages of the website. If none of those vendors carry it perhaps one knows who does.

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