Convergent tip-to-base widening of water-conducting conduits in the tallest bryophytes

Background: Tip-to-base conduit widening is considered a key mechanism that enables vascular plants to grow tall by decreasing the hydraulic resistance imposed by increasing height. Widening of hydraulic anatomy (larger conducting elements towards the base of the vascular system) minimizes gradients in leaf-specific hydraulic conductance with plant height, allowing uniform photosynthesis across the crown of trees. Tip-to-base conduit widening has also been associated with changes in conduit number.  However, in bryophytes, despite having representatives with internal water conducting tissue, conduit widening has been scarcely investigated.

Methods: Here, we examined the changes in hydroid diameter and number with distance from plant tip in Dawsonia superba Grev. and D. polytrichoides R.Br., two representatives of the genus containing the tallest extant bryophytes.

Key results: We found that the position of these moss species on the global scale of conduit size and plant size w...