This is growing in the woods near my house in the Butler, Pennsylvania (USA) area. I have not seen it around before, and I have no idea what is it. What is it? Is it poisonous to pets (or little kids)?
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It only takes a minute to sign up.Sign up to join this community
That looks like a bit like a Smilax to me, possibly Smilax herbacea.
Make sure you have a positive ID on any wild plant before you eat it, but if this is Smilax it looks like you don't have to worry about it being poisonous: from Flora of North America entry on the genus Smilax:
Smilax has numerous uses. Sarsaparilla, a beverage and medicinal used against rheumatism, is obtained from the rhizomes of various species... All species of Smilax are excellent wildlife food and are also browsed, or the rhizomes dug and eaten, by domestic stock.
For you, or for other Pennsylvania people, note that the Pennsylvania Flora Project of the Morris Aboretum is a great resource. You can download species lists by county, and just that and some google image searches can often substitute for a field-guide of your county.
If you want to identify plants the hard way, and are willing to deal with special botanical vocabulary, the Flora of North America that I linked to above is the definitive resource.
I would also guess it's Smilax herbacea, but let me go a step further and explain why...
This does indeed appear to be a species of Smilax, a genus of climbing and sometimes woody plants often found with prickles. The group often picks up the colloquial name "greenbriers," and according to BONAP, 5 of the ~20 North American species are present in Pennsylvania with 4 found in Western PA specifically: S. glauca, S. herbacea, S. hispida, and S. rotundifolia (with S. pulverulenta found in Eastern PA).
Range map of Western PA Smilax species. Sourse: BONAP
Greater detail of the leaves would be quite beneficial for IDing to a specific species, but we'll try to figure this out with the available data. The nice shots of the umbel-shaped infructescences (i.e., the umbrella-like cluster of berries) are certainly useful. The long length of the peduncle (or main shoot to the base of the fruit cluster) should be able to help us here.
If we take a look at Weakley's Flora of the Southern and Mid-Atlantic States (I'm using a 2013 copy), the first dichotomous break in his key references peduncles of either usually > 4 cm long (clearly the case in the OP's picture) or < 3 cm long. Of the species I listed above from BONAP found in Western PA, only S. herbacea falls under the > 4cm peduncle step in the key. In fact, Weakley claims that S. herbacea has
peduncles 5-8x as long as the subtending petioles (these are the small stalks connecting the fruits to the main stalk). BINGO!
peduncle to 30 cm.
But wait, according to both floras above, the berries are supposed to be blue...
Aha! But fruit on many greenbriers often start out paler green before darkening to dark blue in maturity. According to NC State Extension, the berries are not "available" until August in NC, so I'd guess berries in PA would be even farther behind being farther North. If you took this picture relative recently prior to posting the post (mid July), it would suggest any such fruits are still quite immature and so the pale coloration is not totally unexpected (though yours look particularly pale).
Northern Bushcraft (see for additional pictures)
Note: the International Plant Names Index actually lists a number of varieties (though I think a number of these have been separated out as their own species). Gleason and Cronquist (1991) [see here] suggest 3 remain. I point this out simply because some variability could be a result of variation between these different varieties.