I found this plant growing at a neighbours house on my street in Riverdale.The spot is south facing and the attached photo shows that it is about 18″ tall, perhaps 12″ spread. The soil on our street is quite sandy as the photo shows. It is blooming now – early Sept – with clusters of white flowers at the end of the branches.
Thanks for contacting the Toronto Master Gardeners. This plant looks like Euphorbia marginata (Snow on the mountain). It is a self-seeding annual that grows best in full sun and well-drained soil (like the sandy soil on your street). In too much shade it loses its clumping shape. The true flowers are inconspicuous and greenish-yellow, and are surrounded petal-like white brachts (modified leaves). The sap from E. marginata is toxic.
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