Guest Article RHODODENDRON UPDATE 3

  • Date: 12th March 2016
  • author: Francis Crome

INTRODUCTION

This is the third part of our Rhododendron species update and contains 13 species. We have departed from our usual alphabetic ordering of species and have chosen for this update to concentrate on the threatened Rhododendrons (according to Gibbs et al. 2011) that were not covered in the previous two newsletters – one Critically Endangered species, one Endangered and ten Vulnerable.

Our methods are described in the July 2014 newsletter and are summarized in Appendix 1.

For these threatened species we have searched on line to determine whether it is in cultivation and where. Our major sources were the Global Survey of ex situ Rhododendron Collections (BGCI 2011), the Multisite Search page of the Royal Botanic Garden Edinburgh (MSEBG 2014) and the Database of Asian Plants in Cultivation (DAPC 2014).

RATING CONSERVATION STATUS

The conservation rating system is that developed by the International Union for the Conservation of Nature (IUCN) and forms the basis for their Red List. Species are rated as being in one of nine potential categories, depending upon the data available and formal criteria of conservation assessment (Figure 1)1.

Extinction risk increases from Least Concern to Critically Endangered and the three categories Critically Endangered, Endangered and Vulnerable are called the “Threatened Categories”.

Classification into a category is based on five criteria2:

  • Population Size Reduction
  • Geographic Occurrence - This red list criterion uses two terms to reflect distribution – “area of occupancy” is the actual area known to be occupied by the species and “extent of occurrence” is the area of the smallest single polygon that encompasses all these sites (Figure 2).
  • Small Population size and decline
  • Very small or restricted population
  • Quantitative analysis (of probability of extinction)The following summary of the categories is taken from Gibbs et al. (2011).

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