I got lazy and let weeds takeover a bed near the porch that has some azaleas and perennials. When I went to pull some of the weeds, I noticed this ~3ft high plant that looks like a tomato plant. It is starting to fruit and has very small dark, almost black, fruits.
Is this some kind of tomato?
That looks a lot to me like one of the Solanum nigrum ("black nightshade") varieties -- see the "Solanum nigrum complex" paragraph under "Taxonomy" in the Wikipedia article.
I'm not sure where you're from, but they grow as weeds all over North America, as well as -- as far as I know -- most of the rest of the world. They are not tomatoes, and most of these varieties are very dangerous.*
The leaves are smooth and kite-shaped with wavy margins and prominent veins. The berries are clustered and spherical, 1/4" diameter or a bit more at full growth, and turn from green to shiny black as they ripen. The flowers are white and five-petaled, with prominent yellow "beaks" in the center (technically, anthers) . (Personally, I think they're fairly handsome plants.)
It is related to the tomato, as well as several other food plants -- eggplants, capiscums, and potatoes. This accounts for the vague similarites one can see in the fruit and the leaf structures. They are all members of Solanaceae, the "nightshade family".
Some parts of different varieties of this genus and species are reported to have different degrees of edibility, depending on you, the plant, the ripeness of the berries, how you cook it, the day of the week, and whether your car is red.
Please don't eat any part of this plant unless you get a much better identification from an actual botanist or someone who can see the plant first-hand and is verifiably an expert.**
*Among non-mushrooms, poisonous nightshades are probably second only to the poisonous hemlocks ("poison hemlock" and the "water hemlock" genus) in terms of deadliness.
**Actually, that goes for any wild plant. Most aren't poisonous, and most of the poisonous ones aren't automatically deadly, but why make yourself sick for curiousity when there's plenty of books you can check first? Many of the poisonous wild ones are closely related to our food plants -- like this one, and various members of the pea family.
I'd +10 @Bamboo's comment on Brian's answer, if I could: "ID is important". Anyone thinking about eating the berries of something similar should be sure that they don't have Deadly Nightshade, "one of the most toxic plants found in the Western Hemisphere". After giving our daughter ipecac for eating nightshade berries long ago, I always pull up anything that looks like this. I'm sure there are similar plants that are fine; I don't think it's a good idea to have them around to provoke a possibly fatal mistake. Birds spread these around quite a bit (the berries aren't toxic to birds), so if you have it, your neighbor probably will too, sooner or later. Two to five nightshade berries are lethal to children.
The fruit looks like that of Solanum melanocerasum or more commonly Garden Huckleberry.
*Removed comments on eating them just to be safe.*
After looking into this more I found Solanum burbankii, or more commonly Wonderberry, as another edible variety that looks the same as garden huckleberry.
In any case I'd avoid eating them as others have said since it's not known what variety they are and it's probably best to pull them as well. If you would like an edible variety a pack of seeds costs a few dollars and is well worth the purchase to know that you're getting a safe variety.
These grow wild under my pine trees, some people around here say either their kids or their animals eat the black berries, others say they should be avoided at all costs. I confused them for Belladonna aka Deadly Nightshade, but I researched that it doesn't grow on the wild around here, but I read in a local source for anything related to atropa belladona and found out that a very close relative does grow around here. I tried the black berries, ate 5 - 10 of them, and they seem to have a mild sedative effect. Leaf-eating worms seem to love them, so I try to avoid mowing them down when I cut the grass as a means of protecting my potatoes, since it looks like both white flies and caterpillars much prefer these over the potato leaves.
Those arnt the belladonna deadly nightshade, those are edible as long as you eat the black ones not the green ones much the same as how you shouldn't eat green potatoes because of the toxins. They were introduced into Australia as well during the golderush era as vegetables.
