Thorn and hook ontogeny in Artabotrys hexapetalus (Annonaceae)

Artabotrys hexapetalus is widely planted in the tropics and is known as "cl imbing ylang-ylang," an ornamental liana or woody climber: New natural spro uts, or water shoots, and those induced by the damage of Hurricane Andrew ( 24 August 1992) were collected and fixed in formalin/acidic acid/alcohol. S eeds from these plants were planted and grown in a greenhouse where seedlin g morphology was observed and young material collected and fixed. The devel opment of lateral plagiotropic and orthotropic shoots was studied using bot h epi-illumination light microscopy and scanning electron microscopy. A ser ies of buds develops in the;axils of leaves on the orthotropic shoot. Ar th e lateral margins of the axillary shelf, plagiotropic shoots form that will develop into either vegetative shoots, or thorns, or sympodial shoots that bear hooks and flowers. In between the two marginal buds, a series of medi an vertical buds develop that either remain dormant or grow out as renewal orthotropic shoots. Previous work that suggested that the plagiotropic shoo t buds were displaced out of the median vertical series of supernumerary bu ds is not supported. The sympodial development of plagiotropic branches as inflorescence hooks is documented.