Rhododendron maximum leaves are well-known for their propensity to droop & curl in response to freezing temperatures, which is thought to protect the leaves from damage caused by dry, cold air & harsh winter sun. New work by Wang & colleagues investigates the biomechanical properties of Rhododendron leaves that make this phenomenon possible. Their work shows that flexibility of petioles allows the leaves to droop, while leaf veins maintain leaf stiffness during curling. This, combined with the presence of denser & thicker epidermal and palisade layers in more cold-hardy plants effectively alters the mechanical properties of the leaves, allowing for the precise curling & uncurling of the leaves into their characteristic cigar-shaped form. 

Mechanical basis for thermonastic movements of cold-hardy Rhododendron leaves. H Wang, ET Nilsen & M Upmanyu. 2020. Journal of the Royal Society Interface 17: 20190751.
 
Click HERE to read the full article.
 

Leaf morphological, chemical & anatomical traits vary across species, but may also vary within a species according to the climate where the plant grows. Zhang & colleagues investigated the possibility that leaf traits of Rhododendron aganniphum var. schizopeplum differ along an altitudinal gradient above 4200 m in southeast Tibet. They found that plants growing at higher altitude have thicker, more dense leaf tissue, combined with lower nitrogen content. Interestingly, leaf traits for this species appear to be more responsive to a change in altitude compared with other species, indicating that it could be more sensitive to warming climate. This work provides insight into the geography of evergreen species in alpine regions & their responses to future climate change.

Dramatic altitudinal variations in leaf mass per area of two plant growth forms at extreme heights. L Zhang, L Yang & W Shen. 2020. Ecological Indicators 110: 105890.

Click HERE to read the full article.

Find What You Need - Online Resources Page
 

Are you looking for data, images, or opportunities in Rhododendron research?
Do you want to promote a great online research resource?
Our Online Resources for Rhododendron will help you find what you need, fast!

Resources available so far include:

Connect with Us - Social Media
 

A primary goal of our network is to promote Rhododendron research to the scientific community and to the public. In support of this, we have created these new R-RN Social Media opportunities:

 

In an on-going collaboration, members of the American Rhododendron Society & Faculty at the University of Coimbra Portugal are investigating the ploidy level of interploidy crosses. Interploidy pathways are an important mode of hybridization in Rhododendron, but these can result in abnormal seed development.
 
“Pleasant Progress” is a deciduous azalea produced from an interploidy cross of a diploid seed parent (R. cumberlandense × R. viscosum, 2x) by a tetraploid pollen parent (R. colemanii, 4x). This cross is expected to produce triploid offspring, but “Pleasant Progress” is a tetraploid.
 
The triploid siblings appear to be both seed & pollen sterile, while “Pleasant Progress” is both seed & pollen fertile. The interploidy backcross [(cumberlandense X viscosum) (2x) X “Pleasant Progress” (4x)] also produces seed & viable seedlings, indicating further breeding potential.
 
Flow cytometry shows that the siblings of “Pleasant Progress” are triploids, indicating that the likely pathway to “Pleasant Progress” is the production of unreduced gametes by the diploid seed parent, which can happen due to errors during the process of meiosis.
 
Excerpt from upcoming article Pleasant Progress and other interploidy pathways . S Perkins, J Perkins, M Castro, S Castro, & J Loureiro. In press. The Azalean.

Click HERE to access The Azalean.  
 

Auburn University’s Davis Arboretum hosts a unique collection of deciduous azaleas and native evergreen rhododendrons. Patrick Thompson, Arboretum Specialist, describes the great research potential of this collection:

Located on Auburn’s main campus in eastern central Alabama, Davis Arboretum is home to hundreds of accessions with documented provenance from across the Southeastern US. The Rhododendron collection is certified by the Association of the Public Gardens of America’s Plant Collections Network. The flagship species of the collection is Rhododendron alabamense (pictured above), represented by specimens from 5 states and more than 40 counties of origin, a true showcase of the genetic diversity within the species.  Other well-represented species include R. colemanii, R. flammeum, & southern forms of R. cumberlandense. In addition to the species on display, the Arboretum is home to hundreds of unique hand-crossed hybrids.  These selections are the result of 40+ years of selection and breeding by University staff, faculty and local enthusiasts. A handful of these plants have been introduced into the horticulture trade as The Auburn Azalea Series. The series goals were to use locally native R. prunifolium and R. arborescens to breed late blooming plants that stand up to the heat & dry that can be expected from an average summer in the south.     

Click HERE to learn more about Horticulture & Research at Davis Arboretum.

Submit Your Newsletter Items

Submit your news items by December 15 to be included in the January edition.
Jobs, grants, publications, collaborative projects, or any news about Rhododendron research, to: Juliana Medeiros, jmedeiros@holdenfg.org