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Rooting Torreya taxifolia, an Endangered Conifer of the Florida Panhandle

Volume 2 Number 2 - July 1993
Rob Nicholson

Torreya is a primitive member of the Taxaceae, the Yew family. Seven species are known worldwide, 5 species in Japan, Korea and China, one species in California and one species in Florida and Georgia. Torreya taxifolia, the Stinking Cedar, is a rare and endangered species known only from a restricted area of the Florida panhandle and adjacent Georgia.

Beginning in the late 1950s (E.O. Wilson pers.comm.) a sharp decline in the health and reproductive capacity of the native stands was noticed. Since then all full-sized mature individuals have perished and seed production is extremely rare in the wild.

Where trees of 60 feet were formerly found, few individuals over 10 feet are now known. Research into the cause of the decline is ongoing but in situ preservation appears unlikely and management efforts now include the propagation of rooted cuttings from documented wild stands to be grown on in ex situ populations.

For this study, 2,622 cuttings were collected from 166 trees at 14 individual sites from throughout the native range of the species (20 miles north to south, 14 miles east to west). The vigor of individual trees varied greatly and the majority of those sampled were under six feet. The number of cuttings harvested varied with each tree, the overall health of the specimen determining the number of cuttings it was deemed expedient to remove. As few as 1 to as many as 82 cuttings were taken per plant with the average being 15.79. Each collection from each genotype was given an accession number at the time of collection and this number followed the plant through the propagation cycle. A metal label bearing this number was affixed to the parent tree in the wild. Cuttings were taken in November 1989, and transported to greenhouses in Massachusetts where they were given a fungicide soak (Zyban) and then propagated.

Previous trials with Torreya cuttings (Nicholson, 1987) had experimented with various rooting hormones and hormone strengths and had produced a topmost rooting percentage of 65%. In an attempt to increase this percentage, different rooting media were compared and the hormone strength was doubled from 5,000 ppm IBA (Indolebutyric acid) to 10,000 ppm IBA in 50% ETOH. 666 cuttings from 45 different genotypes had the bottom inch and a half of needles removed from the stem , given a fresh cut, and then had this basal portion immersed in the 10,000 ppm IBA solution for 5 seconds. These were then stuck under a poly tent in a medium of coarse builder's sand and medium grade perlite (1:1 by volume) and bottom heated to 75oF. 1,848 cuttings from 121 different genotypes were treated in the same manner, with the exception being a rooting medium of #10 grade crushed pumice, shredded peat moss and medium grade perlite (6:2:1 by volume) was used.

Cuttings were evaluated after six months and potted on. Overall rooting percentage of those cuttings stuck in the sand/perlite medium was 79.2%, while those cuttings stuck in the pumice/peat/perlite mix rooted at an overall percentage of 90.8%.

Roots were analysed in detail for all cuttings stuck in the sand/perlite mix and for an equivalent number of randomly selected cuttings from the pumice mix.

Data recorded were:

  1. number of main roots (roots originating from the stem
  2. total number of root tips (main and branch)
  3. longest root
  4. total length of roots

The results of this analysis are given in Table 1.

TABLE 1                                      

 Sand/perlite mix
 Pumice mix
 Average main roots
2.9
2.4
 Total root tips3.44
5.09
 Longest root average6.37cm  
10.26cm
 Aggregate length average12.98cm
16.92cm
Highest values recorded  
 Main roots1310 
 Total root tips1318 
 Greatest length 
14cm22cm 
 Aggregate length
42cm49cm 

                                                 
A comparison of these two media showed that the pumice mix yielded a higher percentage of rooted cuttings, and a better branched root system of greater total length.

Cuttings were potted and grown for two years and then shipped to botanic gardens and biological research institutions worldwide.

At this time, to simplify the morass of inter-institutional accessioning systems("my 1049-89 is your 222-91A"), each genotype was given a "population identifier", a name similar in use to a cultivar name but signifying the individual genotype and its wild source locale. As an example, Torreya taxifolia "Flat Creek 1" was the first collection at that locale. All inter-institutional exchanges (should a genotype be lost) would therefore be greatly simplified.