Right. IF carbon sequestration is the goal, then corn or algae is not much help. Corn, for example, grows rapidly, taking in lots of CO2, but, within a year (roughly), that corn or it’s derivatives are almost all decomposed, digested, burned (ethanol), etc., putting nearly as much CO2 right back into the atmosphere. The total “reduction” of CO2 is negligible. Algae’s cycle is usually faster.
OTOH, trees produce oxygen from CO2 and can store the carbon for a long time. My vote might go to Black Walnut: We have one in our yard that is growing nearly 4’ a year (good soil, plus nutrients & moisture from a nearby septic system). When we had our big ice storm in 2009, it was the only tree of any size in the neighborhood that was not seriously damaged. And, when the time comes for that tree to come down — it is already at almost harvestable size — it will produce wonderful wood for furniture that with care can last for generations. A slight “ding” (only so far as carbon storage is concerned) is the mass of large nuts (and their husks) it produces in the fall. Well, that and not turning an ankle on a nut!
Of course, even long lived trees’ lives are only an eye-blink in time compared to geologic time scales and processes, which are the REAL storers of CO2. Earth would have an atmosphere much like Venus, but luckily most of our CO2 is held in rocks.