What are the different antenna types used by various IEEE 802.11 standards?
Communication standards usually, and especially 802.11, do not specify antennas. So, there's no "standard antennas".

Which antenna you use depends on your use case; and in the case of WiFi and similar technologies, using highly directive antennas makes no sense, since you can't know in which direction your communication partner is, seeing that usually at least one part of a link is somewhat mobile, and seeing that the WiFi environment often relies on non-line-of-sight links.

Antenna design usually is a relatively experience-heavy field, which not only incorporates the physics of the wave you're working with (that being, almost exclusively, carrier frequency range, and maybe device impedance), but also things like package geometry, cost, weight and size restrictions, aesthetical and ergonomic properties. The standard only defines carrier frequencies/bandwidths. Therefore, it would be illogical to define what antenna to use (you might be misunderstanding what an antenna does, maybe?).

So, your question is inanswerable.

Regarding MIMO: For MIMO to yield a gain, you'll either need the ability to steer a beam (in which case you wouldn't want overly directive antennas in the first place), or to have diversity gain, i.e. uncorrelated channel realizations on individual antennas (and using antennas that are very directive doesn't make much sense here, either, since you might be getting uncorrelated channels easier that way, but also get a high per-antenna outage/deep fade probability, which is the opposite of what you'd want).