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tokens: of a magnetohydrodynamic (MHD) fluid is that weak collisionality permits approximate conservation of particle adiabatic invariants and so when frozen-in magnetic field is locally increased or decreased by the plasma motions, perpendicular ( p ⊥ ) and parallel ( p ∥ ) pressures evolve differently (Chew, Goldberger Low 1956 ; Kulsrud 1983 ), giving rise to local pressure anisotropies. Pressure-anisotropic plasma is unstable when the relative pressure anisotropy is large enough compared to 1/β (otherwise Lorentz forces stabilize the plasma), namely, (the mirror threshold given here is approximate; see Hellinger 2007 ). These instability conditions are easily achievable in the ICM (see Schekochihin et al. 2005 and references therein). The instabilities are very fast in time and microscopic in space compared to any conceivable macroscopic dynamics because they happen essentially on ion Larmor scales. It is reasonable to expect that their effect will be to keep the plasma locally (at most) marginal with respect to the conditions ( 3 ) and ( 4 ); solar-wind measurements lend strong support to this expectation (Hellinger et al. 2006 ; Bale et al. 2009 ). In order to make that happen, the firehose and mirror fluctuations must impose an upper bound on the effective rate of change of the magnetic field (which gives rise to the pressure anisotropies) and/or increase the effective collisionality of the plasma (which relaxes the anisotropies) – either scenario can lead to macroscopic dynamics dramatically different from the conventional MHD evolution. This topic was discussed at length (if speculatively) by Mogavero Schekochihin ( 2014 ), with particular focus on the question of how, under pressure-anisotropic conditions, the magnetic field might be able to grow from a weak primordial seed (believed to be anywhere between 10 −21 and 10 −9 G, corresponding to β ∼ 10 32 − 10 8 ; see review by Durrer Neronov 2013 ) to its observed value ( B ∼ 10 −6 G, β ∼ 10 2 ), even as the rate at which it is allowed to change locally is constrained by the condition where ν eff is either the Coulomb collision frequency or some effective collisionality determined by particle scattering (if any) off microscopic firehose or mirror fluctuations (see further discussion in Section 4.2 ). This is the question of plasma dynamo – magnetogenesis in a weakly collisional turbulent plasma. Besides being of astrophysical (origin of observed fields) and fundamental (what happens?) physical interest, it is likely soon to be attacked not just theoretically, but also experimentally, with the advent of laboratory experiments aiming to reproduce the plasma dynamo process (Spence, Reuter Forest 2009 ; Meinecke et al. 2014 , 2015 ; Forest et al. 2015 ; Plihon et al. 2015 ). The first demonstration of this process in a 3D kinetic numerical simulation by Rincon et al. ( 2016 ) has indeed confirmed the ubiquitous appearance of mirror and firehose fluctuations, although a detailed investigation of