Petty Spurge, Euphorbia peplus
I was born in and grew up in Hayes, Bromley, Kent, a southeastern suburb of London, England. All through my childhood, in our backyard, Petty Spurge was a common, and aggressive, weed species. I asked my mother what it was called. My mother had grown up in a village in Devon, England, and being a country girl, she knew, and had taught me, the names of about 20 or 30 different wildflowers and weeds, but she did not know the name of this one.
As a kid I used to help in the garden, including pulling out the weeds, so I pulled these out, but I always thought that this plant was attractive and exotic-looking, with its pale apple-green foliage and four-fold symmetry.
Here is an observation of the plant from Downe, Kent, about 5 miles from where I grew up, in a village I often visited because Charles Darwin lived there:
https://www.inaturalist.org/observations/31123799
And one near Hayes:
https://www.inaturalist.org/observations/64818725
After I left home, and after I started living in the US, I had not really seen this weed again, or perhaps never noticed it, until September 2018, when to my surprise I came across it in Encinitas, Southern California, near the motel where we stay almost every year. I discovered that the plant was not only present, but common. I made 5 observations of the species, including this one:
https://www.inaturalist.org/observations/16870691
Then in the following month, October 2018, never having seen this plant in NYC before despite all my intense iNatting, I was amazed to find eight examples growing wild as weeds in a flower bed in Battery Park, at the southern tip of Manhattan. I live on Manhattan's Upper East Side, a few miles away from Battery Park. Of course I made iNat observations of all the plants, including this one:
https://www.inaturalist.org/observations/17628788
In June of 2019 I went back to look for the species in Battery Park, and found several examples of it, including this one:
https://www.inaturalist.org/observations/28522420
In July 2019, I also found one plant in Bowling Green, which is a small and venerable park just north of Battery Park:
https://www.inaturalist.org/observations/28522612
In September 2019, when my husband and I went to California again, I photographed 15 examples of the plant in Encinitas, California. And November 2019 I photographed six plants in Battery Park, Manhattan again.
During 2020 I was not able to find the plant in Battery Park, and I did not come across it anywhere else in NYC, despite the fact that I look very carefully everywhere I go for interesting weeds.
However, Daniel Atha of NYBG has found Euphorbia peplus once in the Bronx Park near the NY Botanical Garden. in June 2019 (he collected that one):
https://www.inaturalist.org/observations/26452132
And Daniel also found the plant once in Central Park, in July 2020:
https://www.inaturalist.org/observations/54802168
The Wikipedia article on Petty Spurge,
https://en.wikipedia.org/wiki/Euphorbia_peplus
When it was accessed in October 2020, Wikipedia informs us that:
"Euphorbia peplus (petty spurge,[1][2] radium weed,[2] cancer weed,[2] or milkweed)[2], is a species of Euphorbia, native to most of Europe, northern Africa, and western Asia, where it typically grows in cultivated arable land, gardens, and other disturbed land.[1][3][4]"
"Outside of its native range it is very widely naturalised and often invasive, including in Australia, New Zealand, North America, and other countries in temperate and sub-tropical regions.[1]"