Using the Lellinger and Taylor system, the following patterns are found in Isoetes microspores: aculeate, with bullae (radially symmetrical, low protuberances), no higher than wide, with a broad base and acute apex; cristate, with walls that are narrow, sharp edged, and nonanastomosing; and echinate, with stelae (radially symmetrical, high protuberances) higher than wide, conical, widest near base.
Lateral and medial pronotal carinae absent, except in the females of Lempira and Pararhicnoderma, where the median carina is somewhat nodular, or in Cristobalina & Mayalina, where it is cristate and toothed.