Gelatinous fibers and variant secondary growth related to stem undulation and contraction in a monkey ladder vine, Bauhinia glabra (Fabaceae).
OBJECTIVE
Some of the most striking stem shapes occur in species of Bauhinia (Fabaceae) known as monkey ladder vines. Their mature stems are flattened and develop regular undulations. Although stems have variant (anomalous) secondary growth, the mechanism causing the undulations is unknown.


METHODS
We measured stem segments over time (20 mo), described stem development using light microscopy, and correlated the changes in stem shape with anatomy.


RESULTS
Growing stems are initially straight and bear tendrils on short axillary branches. The inner secondary xylem has narrow vessels and lignified fibers. As stems age, they become flattened and increasingly undulated with the production of two lobes of outer secondary xylem (OX) with wide vessels and only gelatinous fibers (G-fibers). Similar G-fibers are present in the secondary phloem and the cortical sclerified layer. In transverse sections, the concave side of each undulation has a greater area and quantity of G-fibers than the opposite convex side. Some older stems are not undulated and have less lobing of OX. Undulation causes a shortening of the stem segments: up to 28% of the original length.


CONCLUSIONS
Uneven distribution of G-fibers produces tensions that are involved in the protracted development of undulations. While young extending shoots attach by lateral branch tendrils, older stems may maintain their position in the canopy using undulations and persistent branch bases as gripping devices. Flattened and undulated stems with G-fibers produce flexible woody stems.
Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada.
Jack B
JB
Fisher
Mario A
MA
Blanco
D036481:Bauhinia / Q000033:anatomy & histology / Q000254:growth & development*; D003364:Costa Rica; D052585:Phloem / Q000033:anatomy & histology / Q000254:growth & development; D018547:Plant Stems / Q000033:anatomy & histology / Q000254:growth & development*; D052584:Xylem / Q000033:anatomy & histology / Q000254:growth & development
Bauhinia; G-fiber; Phanera; Schnella; anomalous secondary growth; gelatinous fiber; liana; reaction wood; stem contraction; tension wood; vine