Identify garden shrub, spear shaped leaves, 20-25 cm long

Question

Can anyone identify these shrubs in my English midlands garden? They've been there for over 20 years, growing in the shade. I pull them up and they grow back the next year. The leaves are 20-25 cm long by about 15 cm wide. The shrubs are about 65 cm high. The leaves are deep green. One shrub has white veins in the leaves, the other is plain green. There are white lily like flowers in the lower parts of the shrubs. Are they poisonous to dogs?

Answer 1

This is definitely an arum. I agree with Bamboo that it's probably Arum italicum, although it could be a similar species of Arum such as A. maculatum. Regardless, the answer to the question of "Are they poisonous to dogs?" is YES.

Arums have insoluble calcium oxalate crystals in all parts of the plant. If a dog (or other pet or human) eats part of an arum plant, those calcium oxalate crystals will cause immediate pain and irritation in the mouth. A reasonably cautious individual will be warned off by the immediate pain, and will spit out the plant and try to wipe or wash out their mouth; but dogs are not always cautious. If they swallow the plant, the same crystals can cause irritation in the throat and stomach. In the worst case that can make the throat close up, and the dog can suffocate if you can't get them to emergency veterinary care in time. (Also the stomach irritation can cause vomiting, and vomiting + throat closure are a bad combination.)

The question of whether this plant is actually dangerous to your dog depends entirely on whether your dog actually eats it, and whether they will gobble down a lot all at once, or nibble cautiously then spit it out immediately when it hurts. And then whether they will learn from a mistake, or keep repeating it endlessly. If you can't get rid of the plant, keep your dog away from it unless/until you can be confident that they won't eat it. (Can you really ever be sure a dog won't eat a thing?)

If you want to get rid of it, I suggest digging out as many of the bulbs as you can find. Be sure to wear gloves and long sleeves to protect your skin from the sap, which can cause skin irritation. Probably the easiest time of year to do this is in winter or early spring, when it still has leaves firmly attached to the bulbs, so you can find the bulb by pulling gently on a stem while loosening the nearby soil with a shovel. You can also try putting a heavy tarp down over the area before it comes up, and leaving it in place for the entire time the Arum would normally have above-ground growth. Monitor around the edges of the tarp and cut back or dig out any plants that manage to sneak out past the edges.

Italian arum is invasive in North America, so there are a lot of guides for getting rid of it; I linked a couple of them below if you want more information. There's not a lot of info on what herbicides would kill it, but in my experience it takes multiple applications of a systemic herbicide, over the course of several years, to effectively kill off ephemeral perennial like this (IE, a plant that comes up at the same time every year from bulbs or corms or tubers, stays for a few weeks or months, blooms, then dies back and spends the rest of the year dormant underground). If you want to try herbicide, make sure it's a systemic herbicide like glyphosate, imazapyr or 2,4-D. A contact herbicide (IE, one that just kills the leaves) won't do anything to kill the bulbs.

Additional information:

• Here's a good article about arum poisoning in dogs. (It's specifically about Arum palaestinum, but Arum italicum has the same toxin and should be similar.)
• The ASPCA article about A. maculatum poisoning in dogs.
• The Wikipedia page about A. italicum.
• An article about how to get rid of A. italicum.
• Another article about getting rid of A. italicum.

Answer 2

Most likely Arum italicum but the leaves look rather discoloured, pale and somewhat yellowish. Have you applied weedkiller at all, or maybe its suffered because of the long dry spell throughout end of March and April..its an Arum of some description for sure, as is the one with plain green leaves.

It is not a shrub, Arum are tuberous rooted herbaceous perennials which disappear altogether in winter and which grow in shadier, damp places. Had you left the flowers in situ, a spike with red berries would have appeared later - the berries and all parts of the plant are not exactly poisonous if consumed, but they do contain oxalate crystals - one nibble would be enough to deter further consumption because the crystals cause pain, so as long as you aren't going to make a salad with them, they're fine. This link https://www.wildfooduk.com/edible-wild-plants/lords-and-ladies/ provides useful info on Arums generally.

Unless you have a puppy or young children who are prone to eating plants in the garden, you don't need to worry about the toxicity too much - over fifty percent of plants grown in the average UK garden are toxic if ingested. You can dig them out or at least reduce them - just make sure you dig deep enough to lift the tuberous roots.