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Observations on the Propagation of Cupressus dupreziana Camus, an Endemic Saharan Gymnosperm

Volume 3 Number 3 - February 1999
Rob Nicholson, Garcia Bibiana, Bailo McDaniel & Cary MacRay

Cupressus dupreziana, commonly called "Saharan cypress," is an extremely rare coniferous plant belonging to the Cupressaceae. C. dupreziana is one of the 20 to 25 species in the genus Cupressus, most are trees and many are characterized by restricted ranges. Closely related to Chamaecyparis, Cupressus plants are fast-growing trees often found in hot, arid regions, and are present both in the Old and New World.

The Saharan cypress is native to a small, dry, mountainous region of the central Saharan desert in south east Algeria. Very few trees remain alive in their natural environment. In fact, in 1985 only 160 specimens were found in Algeria and C. dupreziana is considered to be one of the world's 12 rarest trees. The 1997 IUCN Red List gives the species a ranking of critically imperiled (E). Some of these trees are estimated to be over 3000 years old and are the last remaining vestiges of a forest assemblage that existed during the moister and cooler Pleistocene epoch. This remarkable age makes this wild population a valuable resource for dendroclimatological research.

The conservatory collections of the Smith College Botanic Garden include two trees that were grown from seed collected by Nicholson in 1985 on the Tassili-n-Ajjer Plateau, an area famous not only for the Sahara Cypress but for thousands of prehistoric cave paintings. We sought to propagate rooted cuttings from our two plants so that we could distribute this rare plant to other botanic gardens for study and preservation purposes. Cuttings from each clone were stuck during early winter (12/15) with a total of ten treatment options used on each clone. One group of cuttings was stuck in a medium of coarse sand and perlite (1:1 by volume), placed in a cool greenhouse 45-60 ºF., on an open bench, and received no bottom heat (I). These were watered whenever the medium appeared dry. The second set was stuck in the same medium but was placed in a greenhouse heated to 60-75 ºF., under an intermittent mist system with bottom heat to 70 ºF (II).

The five pretreatments of the cuttings included a control (no hormone), 24 hour basal soaks in 500 ppm or 1000 ppm Indole Butyric Acid (potassium salt), or 10 second basal quick dips in 10,000 or 20,000 ppm Indole Butyric Acid (potassium salt). After six months these cuttings were examined for the percentage of those that rooted and the average number of roots per cutting for each treatment.

Vegetative Propagation of Cupressus dupreziana

Percentage rooting of stem cuttings and average number of roots per cutting (10 cuttings per treatment).

The cuttings of the tree did very poorly under the first set of conditions-none of them rooted, even though they were treated with various concentrations of Indole Butyric Acid. However, they rooted successfully under the second set of conditions. The cuttings of Clone A soaked in a 500 ppm and 1000 ppm IBA solution for 24 hours were the most successful of their group, with 90 % rooted each. The results for clone B show that in this group the 500 IBA conc. (24-hour soak) was also the most successful (70% rooted), but, unlike in clone A, the 1000 IBA conc. soak was not very successful (30% rooted). Despite this, the 500 and 1000 IBA conc. 24-hour soaks were overall the most successful. They had combined clone A and B percentage rooting of 70%, versus 45% percentage rooting for combined 10,000 and 20,000 IBA conc.10-second dips, and 50% for combined control cuttings.

These results allow us to make the following observations:

  1. Cupressus dupreziana cuttings rooted successfully under intermittent mist with ambient temperature of 60 to 75 ºF, when they were provided bottom heat. However they did not root in a drier,cooler environment in which they were not provided with bottom heat.
  2. An Indole Butyric Acid treatment consisting of a slow, 24-hour soak of the cutting at a low concentration (500 to 1000 ppm IBA) produced better rooting than the treatment consisting of a fast, 10-second dip of the cutting at a high concentration (10,000 to 20,000 ppm IBA), and was more successful than a control treatment where no IBA hormone was provided.

The data obtained from this experiment gave us valuable insight on the most effective method of propagation for Cupressus dupreziana. We are now able to suggest more reliable conditions for vegetative propagation of this endangered coniferous species, making the spread and cultivation of new specimens worldwide more successful and easier than it had been in the past. The plants resulting from this experiment were grown for two years and sent to the Huntington Botanic Garden in San Marino, California for further distribution in a more amenable climate. Botanic Gardens interested in receiving unrooted cuttings can contact the authors at Smith College Botanic Garden.

 
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