Practice question

Hydraulic anatomy surveys across vascular plants show gymnosperm lineages except Gnetales lack true xylem vessels defined by perforated end walls stacking into continuous low-resistance conduits. Tracheid-only conduction limits conduit diameter, constraining leaf lamina size and photosynthetic capacity and transpiration rates, correlating with needle adaptation. Angiosperms overwhelmingly possess vessels enabling efficient transport supporting broad leaves, high vein densities and rapid growth, though primitive Amborella secondarily vesselless. Dicots and monocots both generally vessel-bearing. Therefore textbook statement vessels absent in gymnosperms remains classical diagnostic differential despite Gnetophyte exception representing convergent acquisition via independent evolution.