Dichotomous venation and anastomosis in the corolla of an orchid—Habenaria dentata (SW.) Schltr

Abstract

The lip of the corolla inHabenaria dentata (Sw.) Schltr. is tripartite. The lateral lobes show dichotomously branched veins. While the majority of the vein-endings are related to crenulation in the corolla and terminate at the tip, others end blindly. Usually each crenulation receives one vein. In exceptional cases two veins enter a crenulation. Cases of veins ending beneath an incision (sinus) separating two crenulations have been observed. Sinus vein dichotomies are present. Nine types of anastomoses are described. In Type I, two branches of a single vein-dichotomy remain united. Type II is characterized by the union of adjacent branches of two vein dichotomies and their separation. Type III is similar to Type II but the branches do not separate after confluence. In Type IV an arcuate vein unites with the branch of contiguous vein dichotomy and then separates. Type V is similar to Type IV but the fused branches do not separate. Type VI is formed by the union of the outer branch of a second order vein-dichotomy and the outer branch of a first order vein-dichotomy. In Type VII one outer branch each of two adjacent second order vein-dichotomies unite and separate. Type VIII is similar to Type VII but the branches do not separate after confluence. In Type IX the outer branch of a third order vein-dichotomy and the outer branch of a second order vein-dichotomy unite and separate after a short area of confluence. Cases of vein-approximations also have been observed.