Functional anatomy of the secondary xylem of roots of the mangrove Laguncularia racemosa (L.) Gaertn. (Combretaceae)

We describe the secondary xylem anatomy of three types of roots produced by Laguncularia racemosa (cable roots, pneumatophores and pneumathodes). Formation of lateral roots (pneumathodes) by pneumatophores causes structural modifications in their secondary xylem, like circular vessels, which may have consequenccs for water transport. These modifications are not found in the secondary xylem of cable roots. The path followed by water in the secondary xylem of cable roots and pneumatophores was established by infusion with safranin and by mold-casting with polystyrene. Hydraulic ((k)h) and specific (k(s)) conductivity of the different root types was also determined. We found that the circular vessels at the junctions did not impair k(h) or k(s) values under well-watered conditions, but perhaps the junctions limit water loss when the air-exposed pneumatophores dry out.