AOBPreview originally published online on June 18, 2007
Annals of Botany 2007 100(2):315-324; doi:10.1093/aob/mcm111
Variable Wood Formation and Adaptation to the Alpine Environment of Ephedra pachyclada (Gnetales: Ephedraceae) in the Mustang District, Western Nepal
1 Tsukuba Botanical Garden, National Science Museum, Tsukuba, Ibaraki 305-0005, Japan
2 Forestry and Forest Products Research Institute, Tsukuba Norin PO Box 16, Ibaraki 305-8687, Japan
3 Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
* For correspondence. E-mail noshiro{at}ffpri.affrc.go.jp
Received: 25 January 2007 Returned for revision: 26 March 2007 Accepted: 23 April 2007 Published electronically: 15 June 2007
Background and Aims: Plants of Ephedra normally have vessels, but are known to become nearly vessel-less in some alpine localities. Previous studies implied that wood formation in Ephedra differs fundamentally from that in dicotyledons in which vessel-bearing and vessel-less taxa are systematically distinct. Using E. pachyclada in the Mustang district of Nepal, growing in an altitudinal range of over 2000 m, variation in wood formation and adaptation to alpine environment was studied in this normally vessel-bearing species.
Methods: Variation in wood anatomy and wood formation was observed with conventional optical microscopy. The lengths of three kinds of tracheary elements were measured and statistically analysed against habitat altitude and plant size of the individuals studied.
Key Results: In E. pachyclada three kinds of tracheary elements, vessel elements, tracheids and fibre-tracheids, were nearly equal in length within individuals showing no elongation after differentiation from cambial initials. Tracheary element lengths among individuals had a negative correlation with altitude and a positive correlation with plant size. Multivariate analyses showed that altitude has a stronger correlation with tracheary element lengths than plant height or stem diameter. Moreover, several individuals from high elevations completely lacked vessels, and vessel formation fluctuated even in individuals from lower elevations.
Conclusions: Wood anatomical trends in E. pachyclada are considered as an adaptation to extremely dry conditions in high mountains. Fluctuation in vessel formation in individuals from low elevations indicated that vessels differentiate only when their lateral expansion is allowed. These results showed that E. pachyclada has a different system of wood formation from dicotyledons and supported the opinion that the wood structure of Gnetales is fundamentally different from that of angiosperms.
Key words: Ephedra pachyclada, Gnetales, habitat altitude, plant height, stem diameter, tracheary element length, vessel loss, wood formation