Prickly Lettuce, China Lettuce, Compass Plant, Horse Thistle, Wild Lettuce

Lactuca serriola

lak-TOO-kuh  ser-ee-OH-luh

Synonyms of Lactuca serriola (37) (Updated on 12-2-23 from Plants of the World Online): Hieracium lactuca E.H.L.Krause (1906), Lactuca albicaulis Boiss. (1875), Lactuca altaica Fisch. & C.A.Mey. (1846), Lactuca angustana All. (1773), Lactuca angustifolia Lam. ex Steud. (1821), Lactuca auriculata Aitch. (1882), Lactuca bracteata Wall. (1831), Lactuca coriacea Sch.Bip. (1842), Lactuca dubia Jord. (1851), Lactuca elata Salisb. (1796), Lactuca integrata (Gren. & Godr.) A.Nelson (1909), Lactuca latifolia Gilib. (1782)(opus utique oppr.), Lactuca officinarum Crantz (1766), Lactuca plicata Balb. (1813), Lactuca pseudovirosa Sch.Bip. ex Nyman (1879), Lactuca sativa subsp. serriola (L.) Frietema (1996), Lactuca scariola L. (1763)(nom. superfl.), Lactuca scariola subsp. augustanae (All.) Arcang. (1882), Lactuca scariola var. dubia (Jord.) St.-Lag. (1889), Lactuca scariola var. integrata Gren. & Godr. (1850), Lactuca scariola subsp. integrata (Gren. & Godr.) Piper (1906), Lactuca scariola var. integrifolia (Gray) Bogenh. (1825), Lactuca scariola var. nieuwlandii Lunell (1912), Lactuca serriola var. integrata Farw. (1926), Lactuca serriola subsp. integrifolia (Gray) G.H.Loos (2010), Lactuca serriola f. integrifolia (Gray) S.D.Prince & R.N.Carter (1977), Lactuca serriola subvar. plicata Farw. (1926), Lactuca serriola f. serriola (Gray) S.D.Prince & R.N.Carter (1977), Lactuca sylvestris Lam. (1779), Lactuca sylvestris Garsault (1764)(not validly publ.), Lactuca sylvestris var. integrifolia (Gray) Dumort. (1827), Lactuca tephrocarpa K.Koch (1851), Lactuca verticalis Gaterau (1789), Lactuca virosa Lucé (1823)(sensu auct.), Lactuca virosa var. integrifolia Gray (1821 publ. 1822), Wiestia spectabilis Sch.Bip. (1841)

Lactuca serriola L. is the accepted scientific name for the Prickly Lettuce. It was named and described as such by Carl von Linnaeus in Centuria II. Plantarum in 1756.

The genus, Lactuca L., was named and described by Carl von Linnaeus in the second volume of the first edition of Species Plantarum in 1753.

As of 12-2-23 when this page was last updated, Plants of the World Online by Kew lists 114 species in the Lactuca genus. It is a member of the plant family Asteraceae with 1,702 genera. The number of genera in the family fluctuates quite often.

The above distribution map for Lactuca serriola is from Plants of the World Online. Areas in green are where the species is native and purple is where it has been introduced. The map on the USDA Plants Database for North America is the same.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

THERE ARE SEVERAL LINKS BELOW FOR FURTHER READING AND TO HELP WITH A POSITIVE ID.

There are always quite a few Lactuca serriola growing on the farm but mainly around buildings and fences. I have seen these plants since I was a kid but I hadn’t gotten around to identifying them until 2021. It was just one of “those plants” I suppose I just took for granted. I was keeping my eye on a good-sized colony in the corral in 2021 so I could get photos of their flowers. However, the deer had other plans and ate the tops out of them. I knew there were plenty more, so I later took photos of their flowers from a plant growing next to a shed. Even as a kid, I found their leaves to be pretty neat. Common names include Prickly Lettuce, China Lettuce, Compass Plant, Horse Thistle, Wild Lettuce, and possibly others. Compass Plant is a name it shares with Silphium laciniatum…

Lactuca serriola is an introduced annual or biennial species, being native to parts of Eurasia. It is found all across the United States and all along the lower part of Canada and North America. The species borders Mexico, though I haven’t seen any data to support it is found there. 

Plants are found just about anywhere their seeds will germinate along fence rows, backroads, gardens, barn lots, stream banks, pond banks, forest openings, along trails, in pastures, along roadsides and railroads, fields, and in open disturbed areas. The preference is full sun in just about any type of soil and is tolerant of moist to dry conditions. Plants can grow up to 6’ tall or more in favorable conditions. The plants have strong taproots…

Plants I have seen have always been erect, but information says they can also be ascending. Plants grow from single, unbranched stems that branch out where the flowering stems grow. The stems are light green to whitish tan in color, smooth (glabrous), and usually with stiff hairs (hispid) toward the base.

The easily distinguished leaves grow up to 12” long x 4” wide and are kind of blue-green in color, and deeply pinnately lobed, narrowly oblong to ovate in outline. The leaf surfaces are smooth with prickly hairs along the midveins of the lower surface. Leaves have winged petioles (leaf stalks) that clasp the stems, or they can be sessile (no petioles). OH, I almost forgot… The leaf margins have teeth… 

A former accepted variety, Lactuca serriola var. integrifolia, has unlobed leaves. It is considered a synonym of Lactuca serriola at the moment.

The above photo shows where the flowering stems branch out above the leaf axils.

The top of the stem terminates with MANY well-branched panicles with 50-100 flower heads. The branches are surrounded by clasping bracts.

The fertile ray florets (corollas, petals) of the flowers are light to lemon yellow, occasionally bluish or purplish tinged on the outer surface, or may turn blue when dying. The tips of the ray florets are 5-lobed and nearly straight across (truncate). The floral tube is whitish with a ring of hairs at the apex, otherwise smooth (glabrous). Flowers have 5 stamens and yellow anthers (another distinguishing feature of this species). The styles extend beyond the anthers. These flowers have no disc florets. 

The seeds (achenes) are yellowish-brown to grayish-brown, somewhat flattened, with a thread-like beak, bristly toward the tip, etc., etc. I am getting exhausted. The seeds are dispersed through the wind.

The blooming period is from July to October and the flowers last for about a month. 

Believe it or not, Lactuca serriola is a close relative of culinary lettuce and has been used genetically in selective breeding. Its leaves are edible when young but become bitter after flowering.

The goal in 2022 is to get more detailed and better close-up photos… I use one or two magnifying glasses in front of my lens… Practice makes perfect. 🙂

I have enjoyed photographing and learning about the many wildflowers growing on the farm and other areas. The farm is in Windsor, Missouri in Pettis County (Henry County is across the street and Benton and Johnson aren’t far away). I have grown over 500 different plants and identified over 250 species of wildflowers (most have pages listed on the right side of the page). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can vary from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
FLORA OF MISSOURI (GENUS/SPECIES)
FLORA OF NORTH AMERICA (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
USDA PLANTS DATABASE
DAVE’S GARDEN
MISSOURI PLANTS
UNIVERSITY OF MISSOURI-WEED ID GUIDE
iNATURALIST
WILDFLOWER SEARCH
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
PFAF (PLANTS FOR A FUTURE)
GO BOTANY
FLORA FINDER
FRIENDS OF THE WILDFLOWER GARDEN
MARYLAND BIODIVERSITY PROJECT
INVASIVE PLANT ATLAS
YAVAPAI CO. NATIVE & NATURALIZED PLANTS
UNIVERSITY OF WASHINGTON-BURKE HERBARIUM
SOUTHWEST DESERT FLORA
BPLANT.ORG

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos, but I do get behind. We are all a work in progress. 🙂