Complex sentence: Trees and shrubs have young twigs and smaller branches which are quite flexible and older growth (trunks and large branches) which are stiffer, whereas a liana often has stiff young growths and older growth, at the base of the stem, which is more flexible.
Split into simpler sentences: Trees and shrubs have young twigs and smaller branches which are quite flexible and older growth such as trunks and large branches which are stiffer. A liana often has stiff young growths and older growth, at the base of the stem, which is more flexible.