What is this monster thistle-like weed?

Question

What is this monster weed? It grows back every year and I yank it, but I can't dig out the tap root because it's too close to the gas line.

It is in Norfolk, VA, USA in full sun.

I'm kind of curious about whether it will flower, and I decided to let it grow this year for identification. It's over 6 feet (>1.8 m) tall at this time, and looking rather wilted today in the heat.

Reminds me of a thistle, but it doesn't really have that many barbs, and the ones that it has don't prick my finger when I touch them. I don't want to let it grow much longer, because I'm worried about it going to seed and spreading!

It looks like a wild lettuce of some sort. Might need a flower for a positive ID. — Brenn, May 26 '16 at 19:11
I'd probably just cut it, but if you want it gone, and you use such things, consider nailing it with a herbicide since you cannot dig the root. — Ecnerwal, May 27 '16 at 00:29
@Ecnerwal- Out of curiousity, I'm going to let this ugly monster grow for now to see how tall it gets and then cut it before it goes to seed. I will look into herbicides, as you suggest, and see what will work on the root. I have some weedkiller, but now you've gotten me interested in researching herbicides. — Diane, May 28 '16 at 17:47
@Brenn- I added an updated picture below your answer. It's about 10 feet tall, now! — Diane, Jun 05 '16 at 19:57
I love this thing! I have some in my yard in Massachusetts, and the pictures of both leaves and flowers exactly match the link above the pictures in Brenn's answer. I always let it flower, mostly because I let everything flower so the bees and butterflies have more to eat, but also because it's pretty! It looks kind of majestic standing so tall above everything else! After the flowers bloom it does produce a bunch of seeds but I think the ants or something carry them way, because they don't badly multiply in my yard. — Sue Saddest Farewell TGO GL, Aug 26 '16 at 19:31
I don't do herbicides (not criticizing those who do) so if you decide not to go that route, there are ways to get it down before the seeds spread. Either in flower or while the seeds are still stuck to it, cut the stem into sections. Gently remove the heads or seedpods and throw them out. Keep chopping lower and lower until enough of the weight's off that it will pull out of the ground, roots and all! You may need to dig the roots out. That fresh dirt provides food for your yard creatures - fun to watch! If you do let it flower, post a picture! — Sue Saddest Farewell TGO GL, Aug 26 '16 at 19:44
If you want to keep this plant, just simply take the flowers off as soon as you see them forming. And water would help it look far better. If you don't want to keep it and monitoring the flowering/seed making, there is a very quick way...just grab the stem near the bottom and pull it out. Get it away from your utilities, just a rule of thumb. When it grows back, pull it out again before it makes all this photosynthetic growth to store food in the roots. It will soon be starved out. I think that your idea of killing this guy being rude is WONDERFUL. Empathy for plants IS A GOOD THING! — stormy, Dec 05 '16 at 21:58

score 16 · Accepted Answer · edited Aug 26 '16 at 12:53

16

After a bit of research, I believe my suspicion was correct. It seems to me that you have Tall Blue Lettuce (Lactuca biennis).

Wikipedia article:

Lactuca biennis is a North American species of wild lettuce known by the common names tall blue lettuce and blue wood lettuce. It is widespread across much of the United States and Canada from Alaska and Yukon south as far as California, New Mexico, and Georgia.

Lactuca biennis is a biennial herb in the dandelion tribe within the daisy family growing from a taproot to heights anywhere from one half to four meters (20 inches to over 13 feet). There are deeply lobed, toothed leaves all along the stem. The top of the stem bears a multibranched inflorescence with many flower heads. Each head is just over a centimeter (0.4 inches) wide and has many whitish to light blue ray florets but no disc florets. The fruit is a mottled achene about half a centimeter (0.2 inches) long with a brownish pappus.

Facts, characteristics and images: Lactuca biennis (tall blue lettuce)

edited Aug 26 '16 at 12:53

Ken Graham

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answered May 26 '16 at 19:17

Brenn

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@Brenn- I believe you are right! Thank you. Would you like me to wait for it to flower, or can I accept your answer now? I'm going to go ahead and let it keep growing, since it is kind of awe-inspiring! (Tall Blue Lettuce does not appear to be as invasive as the thistle that I was worried about.) – Diane May 26 '16 at 19:41
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Well you did mention that you're worried about it spreading so don't bother letting it flower because they set seed very quickly after they do. If you snap off a leaf and it oozes white latex, you can pretty much bet on having some type of Lactuca and if that's good enough for you, then no need to have a flower ID. – Brenn May 26 '16 at 19:43
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Just checked. It oozed. I kind of wanted to see the pretty blue flowers, but I understand that in this case my curiosity could be a bad thing! ;) – Diane May 26 '16 at 19:50
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Lol. Perhaps snip off the flower buds and try them in a vase indoors? – Brenn May 26 '16 at 20:34
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I probably will do that! We were already considering names for this ugly monster. Feels rude to kill it after taking its picture. – Diane May 26 '16 at 20:37
@Stephie- Thanks for the edit! Didn't know how to get rid of those brackets so that I could add another image. – Diane May 26 '16 at 20:41
Lettuce? So does that mean it's edible? Did this thing just go from "weed" to "free salad"? – Mason Wheeler May 27 '16 at 00:25
@ Mason- Sounds like a fun question to me! Maybe research what you are seeing here, and post it as question of your own? You are welcome to use any photos that I posted here in your own question. (I did see that it is considered to be a narcotic, but I don't have time to research it further, right now.) Good luck! – Diane May 27 '16 at 01:11
@MasonWheeler From what I can recall, tall blue lettuce is one of the rare exceptions to the rule that you should never eat any plant with white sap. Tall Blue Lettuce *can* theoretically be eaten if boiled for 10 minutes or so, but it is bitter. The taller it gets, the worse it gets. If you can forage it before it grows taller than a foot, it can be ok. After that, pass! – K. Alan Bates May 27 '16 at 02:38
@K.AlanBates- Interesting. Didn't know about the white sap rule! (But then again, leaves oozing white sap never looked appetizing to me.) Thanks for the info. Guess I won't be munching on this tall, bitter monster (not that I was tempted to). lol – Diane May 27 '16 at 16:25
@Brenn- lol Here is an updated picture that I had my boyfriend take. :) (I'm 5 feet tall.) I'd still like to see it flower, but I'm thinking that the storm that is brewing may knock it down before that happens. https://scontent.forf1-1.fna.fbcdn.net/v/t1.0-9/13321617_1115419008517629_5626555607261000653_n.jpg?oh=cd68b714643bf24f4b3a84780456a13a&oe=57DB791F – Diane Jun 05 '16 at 19:48
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@Diane Lol. That's nuts! Perhaps you should plant the good kind of lettuce there and see how it does. Sell those beach ball-sized globes of iceberg lettuce for 10 bucks a pop! – Brenn Jun 05 '16 at 20:19
@Brenn- Yeah, right? lol I wish! It's great soil, but it floods here with every rain, so I mostly have my veggies and herbs in planters. The only thing that seems to love it is my Marjoram, which went wild and has spread over the years to become a wonderful, unplanned ground cover in some of my beds! I love it and can it eat year-round. :) – Diane Jun 05 '16 at 20:47
Brenn, where have you been? I made our OWN room in chat...got a few questions for ya! – stormy Dec 04 '16 at 20:37
Hi @stormy. I've been out of town for a week and I will be traveling over the next several days. Not much downtime for me lately but I'll stop in the chat once night as soon as I get a chance! Thanks! – Brenn Dec 05 '16 at 16:22
Just leave me a 'time'? that is convenient or whatever, ain't life and death that is for sure!! – stormy Dec 06 '16 at 06:16

What is this monster thistle-like weed?

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