Schlumbergera Kautskyi

Calculations are based on 12 loci for Christmas cactus and 13 loci for Easter or 18 crop plants (Doebley 1989).

cactus (O'Leary and Boyl

e 1999, 2000)

culling undesirable plants, random loss of alleles, and changes in gene frequencies because of adaptation to the ex situ environment. O'Leary and Boyle (1999) found that a collection of 40 Easter cactus clones (which included field-collected clones, older cultivars, and modern cultivars) exhibit greater genetic diversity than a subset of 13 modern cultivars that make up the bulk commercial production. Isozyme profiles indicate that many of the uncommon al-leles found in older Easter cactus cultivars are not present in modern cultivars. Thus, the reduced level of genetic diversity in modern cultivars results from loss of alleles during breeding and selection.

Other factors tend to preserve the level of genetic diversity in cultivated cacti. Unlike crops like corn or wheat that have been cultivated for millennia, most cultivated cacti have been domesticated relatively recently and thus have not been subject to intensive breeding and selection. For example, field-collected plants of Schlumbergera trun-cata and H. gaertneri were not introduced into cultivation until 1818 and 1882, respectively. Also, most of the economically important cacti are propagated asexually (except for breeding new cultivars), which tends to conserve more of the initial genetic diversity compared to sexual propagation. Moreover, interspecific hybridization is widely practiced with ornamental cacti and tends to increase the level of genetic diversity, as for Easter cactus. Most cultivated clones of Easter cactus are complex interspecific hybrids of H. gaertneri and H. rosea ( = H. X graeseri [Werderm.] Barthlott). Although flower color is quite limited in two progenitor species (H. gaertneri has scarlet-red flowers whereas H. rosea has rose-pink flowers), the flower color range in H.X graeseri includes shades of red, lavender, purple, and pink to salmon and golden-orange (Meier 1995).

Although overcollection is a significant problem that threatens the survival of some wild cacti, the opposite problem occurs for many cultivated cacti, i.e., low genetic diversity due to insufficient collection from wild sources.

Barthlott et al. (2000) reported that all 58 of the species in tribe Rhipsalideae are in cultivation, but eight of these species (Lepisium micranthum, L. miyagawae, Rhipsalis ewaldiana, R. hoelleri, R. juengeri, R. pentaptera, Schlumbergera kautskyi, and S. orssichiana) are likely to be represented by a single clone. Rhipsalis pentaptera, for example, is cultivated in more than 100 botanic gardens (Barthlott et al. 2000), but there is no genetic diversity among cultivated specimens because they are all derived from vegetative propagation of a single plant. The geophyte Echinopsis chamaecereus (formerly Chamaecereus silvestrii; Fig. 8.1) represents another case of restricted biodiversity in cultivated cacti. It is one of the most popular ornamental cacti and is grown for its unique finger-like shoots and bright scarlet flowers. However, all of the E. chamaecereus plants in cultivation apparently originated from one self-incompatible clone (R. Kiesling, personal communication). Low genetic diversity in cultivated cacti restricts the development of new cultivars by conventional plant breeding techniques.

The importance of conserving cultivars of economically useful cacti is often overlooked but needs to be addressed (Given 1994). Cultivars often contain unique assemblages of genes that may be useful for future breeding efforts. Plant breeders rely primarily on cultivars as the genetic resource for developing new varieties (Frankel et al. 1995). Aside from their economic value, cactus cultivars can be useful for both applied and basic research because they often can be cultivated more readily than wild taxa.

Conservation of Cacti

Human activities are having a heavy impact on populations of cacti, whether that impact is the destruction of natural habitats or overcollecting by hobbyists and commercial dealers. Careless collectors have left piles of dying cacti in the field (Fig. 8.2), and mining activities, road construction, and farming have destroyed prime habitat for

Figure 8.1. Echinopsis chamaecereus (formerly Chamaecereus silvestrii), commonly known as peanut cactus, is a popular ornamental species. The plants in cultivation apparently originated from vegetative propagation of a single, self-incompatible clone.

rare cacti. Indeed, cactus conservation faces a serious crisis. Unfortunately, there are few easy answers as to how cacti can be better protected because part of the problem rests with human nature.

Most people agree that conservation is a good thing. Unfortunately, many view conservation strictly in the abstract, not in the biological sense, where it properly lies. Also, there are disagreements among biologists themselves as to the best ways to conserve wildlife. Both plants and animals are part of the ecosystem; all have a function, though we may not easily recognize it. One can speak of the esthetic aspects of wildlife, or of the potential and actual contributions that plants and animals make to human existence, whether for food, fiber, beauty, medicine, or a myriad other things. Thus, most accept the fact that plants and animals should be protected, but some limit that protection to "whenever possible and appropriate." There are continuing struggles between conservationists and developers, between those that want to protect wildlife and those that wish to exploit it. Usually there are not easy answers or simple compromises between these differing par ties. Hence, conservation efforts are frequently frustrated by well-intentioned groups that simply have different agendas. Education and communication are two critical tools that must be used if conservation efforts are to have a chance of success.

Some wish to lock up vast areas of land, restricting access to everyone so that natural populations of plants and animals will be permanently preserved. Others feel that living organisms should be an available resource for humans, and that natural events, such as extinction, should be allowed to proceed, especially when coming in conflict with human activities. Some believe that a few protected areas, botanic gardens, and zoos will be adequate for preserving at lease some of the natural diversity. Unfortunately, whatever conservation approach is used, extinction is irreversible, and the lost organism cannot be brought back again. Interestingly, few would disagree that one of the main functions of conservation is to perpetuate plants and animals so that future generations may benefit from them. The problem is how to best attain that goal. Conservationists often speak of the importance of plants as pos-

Figure 8.1. Echinopsis chamaecereus (formerly Chamaecereus silvestrii), commonly known as peanut cactus, is a popular ornamental species. The plants in cultivation apparently originated from vegetative propagation of a single, self-incompatible clone.

Figure 8.2. Pile of dead and dying cacti in the Big Bend Region of west Texas in 1982. Pictured is Duc Anderson, an assistant on a field study of rare cacti.

sible sources of drugs or other products of value to humans. Clearly, a strong case can be made for the conservation of plants, including cacti.

Why Cacti Are Threatened

Cacti, like many other plants, are seriously threatened by habitat destruction, whether for the development of new farmland, for expanding urban areas, or for other human activities, such as road building and mining. Many cacti are also threatened by collectors, who wish to either sell them in the trade or simply have them in personal collections. Cacti are remarkable organisms, and many people throughout the world enjoy collecting and propagating them. Unfortunately, a source of plants for trading or selling is needed, and this source often comes from wild populations. Millions of cacti are artificially propagated annually, thus satisfying many hobbyists (Fig. 8.3). However, some collectors are like "stamp collectors" in that they want as many "originals" as possible, meaning that the plants must come directly from the wild. Thus, uncommon and unusual cacti are frequently the victims of these unscrupulous collectors, who flout local and national laws to satisfy their personal needs. Conservationists agree that habitat destruction is one of the main factors that lead to extinction, but habitat destruction is only one of the causes of the disappearance of cacti, with illegal collecting being a significant cause.

These illegal activities have been frustrating to scientists. A goal of scientific research is to provide an accurate description of material being studied. However, scientists have quickly learned that unscrupulous collectors immediately visit sites, the descriptions of which have been published or recorded on herbarium sheets. In several instances most or all the plants have been removed, e.g. for Aztekium ritteri. A new locality for this species has been obtained so that it can be studied (Anderson and Skillman 1984); however, habitat information is presented only in broad generalities because of the threat of collectors, a dilemma faced by many researchers. In 1996 George Hinton described a new Mammillaria species, M. luethii. The few plants that have been seen and the photographs of this unusual cactus have caused a sensation among collectors, who wish to learn where it grows. Hinton and Jonas Luthy, the discoverers of the plant, have not told anyone of its location because of its rarity and the near certainty that unscrupulous collectors would immediately devastate the wild population if the location were divulged. Rather, the two are arranging for the artificial propagation of the species to make it available to collectors. Again, however, proper science is thwarted by the need to protect the wild population.

Cactus researchers have long realized the importance of cactus conservation. In 1987 the Cactus and Succulent Specialist Group of the Species Survival Commission (SSC), an arm of the International Union for Conservation of Nature and Natural Resources (IUCN), was created. Scientists from many regions of the world collaborated in writing Cactus and Succulent Plants: Status Survey and Conservation Action Plan (Oldfield 1997). This document is the most comprehensive publication dealing with the conservation status of each succulent plant group, including cacti, as well as conservation measures and action proposals.

Determination of Threatened Cacti

The United States Endangered Species Act was passed in 1973 and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) came into existence in 1976. There was necessarily a rush to place plants that people thought were threatened or endangered on the lists. The first listing of cacti for CITES was creat

Figure 8.3. Commercially grown cacti in California.

Figure 8.3. Commercially grown cacti in California.

ed on 1 July 1975, and in several cases there were few data to support the decisions that were made. Indeed, the determination of what organism is threatened or endangered is difficult at best, but a strong effort has been made to create a useful system by which plants and animals are placed in various categories of threat. Nearly sixty species of cacti are currently listed in Appendix I of CITES (Table 8.3). Thirty species are listed as threatened or endangered in the United States (Table 8.4). This may seem like a small number when considering that there are about 1,700 species of cacti.

Studies of natural cactus populations since 1960 indicate two things: (1) not all seriously threatened cacti are on either of the lists; and (2) not all the plants on the lists may, in fact, be seriously threatened with extinction. The United States government asked scientists at the Desert Botanical Garden in Phoenix, Arizona, to monitor two species of cacti in the Big Bend region of Texas that were listed in the U.S. Endangered Species Act as Threatened: Echinomastus ( = Neolloydia or Sclerocactus) mariposensis and Coryphantha ramillosa (Anderson and Schmalzel 1997; Schmalzel and

Anderson 1999). Both species were found to be widespread and not seriously threatened with extinction. Scientists at the Desert Botanical Garden have also been involved in evaluating the conservation status of suspected rare cacti in Mexico, an effort sponsored by the World Wildlife Fund (Anderson et al. 1994). A joint team of Americans and Mexicans has been involved in a 3-year, CITES-sponsored cactus-monitoring project, also in Mexico (Anderson z997). The two monitoring projects (in Mexico) provided much information about the conservation status of nearly 50 species of rare cacti.

Two new species of cacti, Aztekium hintonii and Geo-hintonia mexicana, were described in 1992 just prior to the beginning of the CITES-sponsored study, so they were initially included in the project because of the excitement produced among the cactus hobbyists and dealers and uncertainty about their conservation status. The discoverer of the plants, George Hinton, provided detailed information about the size and density of the populations of the two species, which grow sympatrically on gypsum rocks in Nuevo León. Both species are relatively widespread and

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment