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Citrus Germplasm 5 страница







 

fruit rind is fragrant. There are usually six (sometimes 4–8) ovules per locule. A new putative species, O. brevipes, was recently published (Stone, 1985b). Although appar- ently not extremely rare in its native south- east Asian archipelagos, this genus is not often found in ex situ collections and is consequently not well characterized horti- culturally. Swingle (1943) speculated that it is xerophytic based upon its leaf morphol- ogy.

 

 

Merope

Merope is a monotypic genus (M. angulata) distinguished from Wenzelia and Monanthocitrus by having four ovaries per locule and large seeds in the triangular (in cross-section) fruit. Merope angulata is a spiny, salt-loving shrub with thick, leathery leaves that grows in tidal marshes in Java, Burma and the East Indian Archipelago. This species is considered salt tolerant due to its habit; this was confi rmed in green- house tests by Swingle (1915a). This genus is not well represented in ex situ collec- tions but probably has useful properties. Jones (1982) reported briefl y on habitat loss affecting this species, as well as certain medicinal uses. Merope is considered threatened by Jones (1990).

 

 

Swinglea

Swinglea, Aegle, Afraegle, Aeglopsis, Balsamocitrus, Limonia and Feroniella con- stitute the Balsamocitrinae, or ‘hard-shelled citroid fruit trees’. This curious branch of the Aurantioideae has large, heavy fruits with a hard, mostly wood-like exocarp. The locules are fi lled with resinous gum and the seeds are sometimes covered with fine hairs.

Swinglea comprises the Tabog group of this subtribe. ‘Tabog’ is a name used for this species in the Philippines. Swingle (1913b) published his description of this monotypic species with the name Chaetospermum glutinosa. It was renamed Swinglea gluti-



nosa by Merrill (1927), who pointed out that Chaetospermum had already been used as a name for a genus of fungus.

Swinglea glutinosa is distinct within the ‘hard-shelled citroid fruit trees’ in having a tough, leathery shelled fruit rather than a hard, woody shelled fruit. The cells of the fruits are lined with spongy tissue and the walls of the locules are lined with large mucilage glands, features not found in other members of the Balsamocitrinae. The seeds are hairy. Swinglea and Burkillanthus are somewhat similar in some external attributes, but have different fruit anatomies.

Swinglea is a small, thorny tree with trifoliolate leaves that is native to Luzon Island in the Philippines. It has been spread throughout many tropical areas, and is not uncommon in ex situ collections. Swingle (1943) states that it is cold-hardy to 35˚ F (1.67˚ C), but it has been diffi cult to estab- lish in the fi eld in Riverside, where winter temperatures are rarely lower than that. Swinglea glutinosa is graft compatible with Citrus, and there has been some horticul- tural characterization over the years (Table 4.3).

 

 

Aegle

Aegle, Aeglopsis, Afraegle and Balsamocitrus comprise the Aegle group of the ‘hard-shelled citroid fruit trees’. They all have hard, woody fruits without longitu- dinal ribs. The locule walls do not have large, evident mucilage glands, but mucilage glands are present. Leaves are simple, unifoliolate or trifoliolate. The ancestral type was presumably from south Asia, but three of the genera (Aeglopsis, Afraegle and Balsamocitrus) ‘migrated’ to Africa, while none ‘migrated’ eastward to the South-east Asian archipelagos.

Aegle is distinct from the other mem- bers of the group in having very numerous (> 30) stamens, a large number (up to nearly

20) of locules in the ovary, and wooly seeds. The leaves are trifoliolate but vari- able in size and other anatomical features.


 

A monotypic genus (A. marmelos), it is deciduous when cold temperatures occur during the winter. It is native to India and has spread from there to adjacent areas. Aegle marmelos can grow to 15 m or more in height in the proper conditions.

Aegle marmelos is the bael fruit of India and adjacent areas. It has a long his- tory of cultivation and use. It is a sacred tree to Shiva and its leaves are used as offer- ings. In addition to being edible, various medicinal uses have been ascribed to the bael (Table 4.3). Swingle (1943) describes large-fruited, cultivated varieties and small- fruited, wild varieties, and speculated that there are different strains of varieties. In fact, in India, there are named varieties; the names are derived from the localities in which it is grown (Singh and Roy, 1984; Roy, 1998). Differences in levels of sugar, mucilage, phenolics and tannins are docu- mented, as well as physical differences such as shell thickness/hardness, fruit size, seediness, etc. Positive qualities are associ- ated with larger fruit, some of which have shells that can be broken with only fi nger pressure.

Although there is apparently genetic diversity present in India, the genetic diver- sity of A. marmelos in ex situ collections is much lower. There have been few introduc- tions to the USA and other Western coun- tries. Most A. marmelos in these collections represents very hard-shelled, medium- fruited examples. Aegle is graft compatible with Citrus and its horticultural properties have been documented (Table 4.3).

 

 

Aeglopsis

Aeglopsis differs from Aegle in having fewer locules in the ovary, fewer stamens, and simple leaves. The fruits are smaller (and the shell less hard?) than those of Aegle and are pyriform. The two species,

A. chevalieri and A. eggelingii, are both native to Africa. Aeglopsis is graft com- patible with Citrus but has otherwise had only limited horticultural evaluation (Table 4.3).


 


Afraegle

Afraegle is also native to Africa, but is more confi ned to the western portion of the con- tinent than is Aeglopsis. Afraegle is similar to Aeglopsis, but has (mostly) trifoliolate rather than simple leaves, a larger number of locules per ovary and slightly less woody shells. Afraegle trees are vigorous. Afraegle is graft compatible with Citrus. There has been little horticultural evaluation done (Table 4.3).

 

 

Balsamocitrus

The monotypic genus Balsamocitrus (B. dawei) is native to central Africa. It is simi- lar to Aeglopsis, but has trifoliolate leaves and larger fruit. Both Aeglopsis and Afraegle were formerly included in Balsamocitrus until split off at different times (Swingle, 1912). Although its geo- graphic distribution in Africa is apparently fairly limited, B. dawei appears to grow well in a fairly wide range of climates when maintained in ex situ collections. It is vig- orous and exhibits more vertical growth, as compared with the more spreading growth of Afraegle. However, it has not had much horticultural evaluation. This is possibly due to the somewhat erratic fruit produc- tion (at least in Riverside). It is graft com- patible with other hard-shelled citrus relatives and is probably graft-compatible with Citrus.

 

 

Limonia

Limonia and Feroniella constitute the dis- tinctive wood-apple group of the ‘hard- shelled citroid fruit trees’. They are distinguished by the fact that the locules fuse during development into a single cavity, which becomes lined with parietal placentae bearing many ovules. The leaves are odd pinnate with paired opposite leafl ets.

Although confusion regarding generic names is by no means rare in the


Aurantioideae, the case with Limonia is perhaps one of the least clear. This is a monotypic genus. Swingle (1914c, 1943) argued for Feronia limonia, stating that Limonia was ambiguous. Airy-Shaw (1939) supported the name Limonia acidissima. Since Swingle wrote the book (Swingle, 1943), Feronia limonia has generally been used. More recently, Panigrahi (1977) accepted Limonia as the genus name but rejected L. acidissima, instead substituting the older species name elephantum, result- ing in L. elephantum. Stone and Nicolson (1978) rejected this and supported L. acidis- sima. Feronia limonia, with F. elephantum as a synonym, is supported by Hortus Third (Bailey Hortatorium, 1976), while Wiersma and Leó n (1999) support L. acidissima.

In any case, these thorny trees are native to India, where they grow in the hills but not to the same elevation as Aegle. The growth habit is curious and somewhat vari- able. The branches often are clustered towards the top of the tree, with drooping branchlets. Other trees have the branches and branchlets spaced at regular intervals up the trunk. The fruits are edible and also have medicinal uses. Limonia is deciduous. Swingle (1943) states that the leaves are dropped in cold weather. However, in ex situ collections the leaves have been observed to drop during the warm periods of the year and even in greenhouses, so per- haps it is more of a generalized stress reac- tion. Although Limonia is present in many ex situ collections and is graft compatible with Citrus, it is not well characterized hor- ticulturally (Table 4.3).

 

 

Feroniella

Feroniella is very similar to Limonia in its leaf and fruit characteristics. It differs in the form of its stamen and in having glabrous rather than pilose seeds. The stamens are unique among the Aurantioideae in having pilose, partly free, appendages at the base of the fi laments, which are much longer than the anthers. This difference is not readily apparent and it is diffi cult to distinguish


 


 

between Limonia and Feroniella.

The four species of Feroniella are native to the South-east Asian peninsula and archipelagos. It is rare (Jones, 1990). Although Swingle (1943) does not state that it is deciduous, in ex situ collections it appears similar in this regard to Limonia. Like Limonia, Feroniella is graft compatible but is not well characterized (Table 4.3).

 

 

Micromelum

The tribe Clauseneae (Very Remote and Remote Citroid Fruit Trees) contains 5 genera: Micromelum, Glycosmis, Clausena, Murraya and Merrillia. The fi rst and last constitute the subtribes Micromelinae and Merrilliinae, respectively; the remaining genera, the subtribe Clauseninae. Swingle (1943) considered the Clauseneae to be primitive members of the Aurantioideae, primitiveness being characterized as: small, semi-dry or juicy berries; odd-pinnate leaves with alternately attached leafl ets; and a lack of spines in the leaf axils. Chemotaxonomy (Kong et al., 1988) suggest that Micromelum is a primitive species that gave rise to the two branches of Murraya and subsequently to other taxa (Glycosmis and Clausena from the Bergera section and Merrillia from the Murraya section).

Micromelum is a genus of about nine species distributed from Pakistan through south and South-east Asia to the archipela- gos. They are shrubs or trees, with com- pound leaves of up to 23 leafl ets. They are distinguished from other members of the ‘very remote and remote citroid fruit trees’ by having cotyledons that are flat and folded rather than thick and plano-convex. The ovaries have a twisting of the radial fol- licle walls. Both of these characteristics are unique in the Aurantioideae.

Swingle (1943) spelled out the species problem in Micromelum as being the vari- ability of characteristics in the described species. In spite of Swingle’s (1943) asser- tion that ‘new characters are being found that promise to make possible the satisfac- tory defi nition and the easy recognition of


 

the species’, little more has been written or published in the last 60 years, and the genus remains obscure. Although Micromelum species are reported in various fl ora, there is little information about their distribution and a lack of references to tax- onomic advances. This genus is not well represented in ex situ collections and needs horticultural characterization.

 

 

Glycosmis

Glycosmis, Clausena and Murraya are the Clauseninae, or ‘remote citroid fruit trees’. These three genera have very simple and primitive fl owers and fruits, which are usu- ally borne in large terminal panicles. This subtribe is ‘typical’ of the Clauseneae, with the Micromelinae and Merrillinae being aberrant.

Glycosmis differs from the Clausena and Murraya in having a persistent rather than deciduous style, in usually having only one rather than two ovules per locule and in having rust-coloured, ferrugineous puberulence on new vegetative growth, infl orescence axes and buds. In addition, Glycosmis has equilateral leafl ets rather than the non-equilateral leafl ets of most Clausena and Murraya species.

In contrast to his treatment of most genera, Swingle (1943) presents a truncated view of Glycosmis. Rather than his usual thorough treatment of even questionable species, he presents only a ‘tentative list of species of Glycosmis ’. This list is simply an enumeration of published names and reported locations. Swingle (1943) admits in his treatment ‘The species of Glycosmis are still very inadequately described and need study more urgently than those of any other genus of the orange subfamily … the taxonomy of Glycosmis is in such a state of confusion that it is not yet possible to key out all the species or even to tell with cer- tainty how many should be recognized as valid.’

Fortunately, relatively recently there has been an extensive revision and updat- ing of Glycosmis by Stone (1978a, 1985b,


 


1994b). The fi rst paper (Stone, 1978a) gives a review of the 95 published species of Glycosmis and the confusion surrounding this genus over several centuries. Much of the confusion revolves around obscure rules for taxonomic nomenclature and the ambiguity in the identity of G. pentaphylla. Stone (1978a) reviews earlier work on Glycosmis by Tanaka (1937), Narayanaswamy (1941), Brizicky (1962b) and Mitra and Subramaniam (1969), after which it is concluded that some older mate- rials and descriptions of G. pentaphylla, the type species, were based instead upon G. mauritiana. This was due to the incorrect application of G. pentaphylla (and its older identifi cation as Limonia pentaphylla) by Roxburgh. The correct name of G. penta- phylla in the sense of Roxburgh is thus G. mauritiana. The G. pentaphylla (and its older identifi cation as L. pentaphylla) of Retzius is considered to be the ‘real’ G. pen- taphylla. Stone (1978a) is supported in this identifi cation by Panigrahi (1985), who also argued that G. pentaphylla and G. arborea are synonyms, and by Huang (1987). The reader is referred to these works for the complete (and complicated) rationale

behind this.

The result of the ambiguity in the iden- tity of G. pentaphylla is that, according to Stone (1978a), many specimens identifi ed as G. pentaphylla will have to be re-identi- fi ed. It is also noted by Stone (1978a) that due to the ambiguity in the identity and description of G. pentaphylla, the concept (his italics) of this species had expanded over time and it became a sort of warehouse for any unidentifi ed Glycosmis collected. Stone (1978a) identifi es at least four species that he believed were mistakenly identifi ed as G. pentaphylla: G. mauritiana, G. citrifo- lia, G. parvifl ora and G. cochinchinensis. In addition to casting doubt on the identity of herbarium specimens of G. pentaphylla, this information also calls into question the identity of some G. pentaphylla (and per- haps other Glycosmis species) found in ex situ collections. The fact that Swingle (1943) correctly identifi ed G. pentaphylla as being the G. pentaphylla of Retzius might


mean that G. pentaphylla as introduced as by the USDA is correctly identifi ed. The identifi cation of G. pentaphylla in ex situ collections needs to be verifi ed.

In the second part of his revision, Stone (1985b) presents a systematic treatment of Glycosmis. In this treatment, he recognized 43 species, of which seven were new (some of these were published previously by Stone). A number of new varieties were also published. Stone (1985b) excludes G. africana, G. bonii, G. cambodiana, G. crenulata, G. harmandiana, G. spinosa and

G. subvelutina. Stone (1994b) discusses some further aspects of his conspectus and also analysed three additional Glycosmis species published by Huang (1987). The conspectus (Stone, 1985b) includes a key to Glycosmis species, which Stone admitted is only ‘fairly close to being a usable key’. The key divides Glycosmis into fi ve groups based upon leaf and fl oral char- acteristics.

The monumental tripartite work of Stone (1978a, 1985b, 1994b) remains the most thorough treatment, with little or nothing being published after that. The death of Stone and other factors make it unlikely that much more will be written defi nitively about this genus in the near future.

Glycosmis is distributed throughout south and South-east Asia, from India through the archipelagos. The species are shrubs and have varying habitats, including limestone soils and riparian areas. Observed Glycosmis species are generally attractive plants, with shapely leaves and small, pinkish-red berries. Most of the pub- lished information on this species seems to involve the taxonomic issues. Glycosmis is represented in many ex situ collections, but species maintained are often limited to G. pentaphylla (but which one?) and in some cases G. parvifl ora. There has been little horticultural characterization of this genus. Small (1933) and Brizicky (1962a) report Glycosmis (but which species?) as being naturalized in south Florida, but this is somewhat doubtful (K. D. Bowman, per- sonal communication, 1999).


 


 

Clausena

Clausena and Murraya differ from Glycosmis in the characteristics noted in the previous section. These species are very similar, but differ from one another in cer- tain ways. Clausena has fl ower buds that are globose or broad-ovoid, never long and slender, while Murraya has cylindrical or long-ovoid fl ower buds. Similarly, the style of Clausena is short and thick, whereas that of Murraya is long and slender. A distinc- tive feature of Clausena is the large, hour- glass-shaped gynophore. This, however, is a somewhat variable characteristic (Swingle, 1943). Molino (1994) bases the key on the same stylar characteristics, the structure of the gynophore and the struc- ture of the stamen.

Swingle (1943) notes some of the same challenges in Clausena taxonomy and nomenclature as in that of Glycosmis: a lack of specimens for examination and variabil- ity within taxa. He was able to borrow and examine nearly a thousand herbarium spec- imens in his study of Clausena. Based upon this study, Swingle (1943) recognizes 23 genera, some of which he had published within a few years of his monograph (Swingle, 1940b, 1942). His key is divided into four parts based upon geographic dis- tribution (basically the Indian subconti- nent; the Indochinese peninsula; the archipelagos; and Africa). To this, a new species (C. calciphila) was added by Stone (1978b).

Molino (1994) based a revision of Clausena on new collections and a greater emphasis on fl oral characteristics, resulting in a collapsing of the genus to 15 species divided into four sections based upon fl oral structure. A new species was described (C. poilanei) and several new names and com- binations were proposed (for instance, the

C. calciphilla of Stone, 1978a, became C. sanki var. calciphila). Most notable was the establishment of synonymy for some of the species. This was especially pronounced in the case of C. anisata, which absorbed four species and seven varieties of Swingle’s (1943) treatment. Clausena anisata became


 

the only Clausena species to be found in Africa and was considered to have ‘migrated’ there relatively recently. Additional species noted by Swingle (1943) were also pulled into other species.

Clausena is widely distributed geo- graphically, from the South-east Asian arch- ipelagos, through the South-eastern and south Asian regions, and north to the sub- tropical parts of China. There are two ‘satel- lite’ areas: Africa, where C. anisata (in the sense of Molino, 1994) is widespread, and north-eastern Australia, where C. brevistyla and the recently published C. smyrelliana (Forster, 2000) are found. Some species are reported to grow at elevations of up to 3000 m, while others are decidedly tropical.

Clausena species range from small shrubs to 20 m tall trees. Molino (1994) states that in areas that are climatically mar- ginal, particularly the two satellite areas, the leaves may be deciduous; this is not noted by Swingle (1943). Observations in Riverside, California, would seem to indi- cate that there is at least some deciduous aspect to the leaves. However, as with the other deciduous types maintained there, the trigger for leaf drop is not apparent. Likewise, fl owering at Riverside is erratic. It is possible that this is due to climatic fac- tors, but Molino (1994) states that fl owering occurs throughout the year in many areas, but with a peak in the dry season. The fl ow- ers are borne on bunches and produce small fl eshy berries surrounded by mucilage.

Several species of Clausena deserve particular mention. Although several Clausena species produce edible fruits, the only one commercially cultivated is C. lan- sium, the Wampee. Clausena lansium is actually quite distinctive among Clausena species, having a star-shaped bud and a fi ve-angled ovary that has hairs on the lat- eral walls of the locules. In addition, there is a central gum canal in the twigs. For additional distinctive characteristics, see Swingle (1943). The Wampee is native to southern China, and that is its main area of cultivation. Cultivation has spread to a very limited extent to the countries around China. The golden-yellow berries, which


 


are borne on large panicles, are the largest of any Clausena species and are eaten fresh as well as being used for preserves. The Wampee is relatively common in ex situ collections, but it is sometimes diffi cult to obtain seeds since the fruits are so irre- sistible to birds. Most ex situ collections have only a small representation of Wampee, but in China there are many local varieties. A few found in Kwantung Province are listed in Swingle (1943), while different named varieties are found in Fujian and Guangxi Provinces (Shu Yuan, personal communication, 1984); there are doubtless others. Wampee is graft compati- ble with Citrus but there are apparently some incompatibility problems since the resulting trees are small and weak (Swingle, 1943; Campbell, 1974). Campbell (1974) stated that cold winters can kill Wampees in southern Florida, but limited experience in the harsher climate of southern California indicates that they can survive temperatures near 0˚ C. In fact, C. lansium seems to be more cold tolerant than other Clausena accessions maintained in Riverside (C. anisata and C. excavata). The Clausena accessions seem more sensitive than the closely related Murraya accessions maintained. It is possible that it is some environmental factor other than cold that makes establishment in the fi eld diffi cult.

A few other species will be mentioned in passing. Several other species produce berries that are harvested from wild trees and consumed locally. These include C. dentata var. dulcis of Madras, India; C. indica of India and Ceylon; and C. dentata var. henryi of south-western China. In the treatment of Molino (1994), C. indica was absorbed into C. sanki and both varieties of

C. dentata were absorbed into C. anisata. Clausena anisum-olens (incorporated into

C. sanki by Molino, 1994) is native to the Philippines, where it grows up to elevations of 1500 m. It is used in the preparation of anisado, an alcoholic beverage, and has a very high concentration of the essential oil anethole, the true anis oil. See Molino (1993) for more information on various specimens of this throughout the world.


Occasionally Clausena species other than C. lansium are found in ex situ collec- tions. However, C. lansium is by far the most common. Consequently, although there has been some horticultural charac- terization of this genus, most of that work has been done on C. lansium, and on a rather limited genetic range of material at that.

 

 

Murraya

Murraya is closely related to Clausena with the differences noted above. Swingle (1943) describes 11 mostly closely-related species. Huang (1978) added M. kwangsiensis. More recently, data of various types has sup- ported the division of Murraya into two species, Murraya and Bergera. Chemotaxonomic studies with alkaloids (Kong et al., 1986) and terpenes (Li et al., 1988) divided Murraya into two groups. The fi rst group (Murraya) possesses yellow- ish stems and roots; fl owers with larger petals (1–2 cm long); and red, ovoid to ellipsoid fruits. The other group (Bergera) possesses brown stems and roots; fl owers with smaller petals (4–7 mm long); and pur- plish-black, globose to ellipsoid fruit (Jones, 1995). Kong et al. (1986) state that this division supports that of Swingle (1943); however, no division of Murraya is noted in either Swingle (1943) or its revi- sion (Swingle and Reece, 1967). This is con- fi rmed by Jones (1995), who then gives the group names cited above, even though they do not appear in Swingle (1943), Swingle and Reece (1967), nor Kong et al. (1986). Recently, this division was reinforced with molecular (Samuel et al., 2001) and kary- otypic (Guerra et al., 2000) analysis. M. koenigii and M. siamensis were separated into the genus Bergera, with the remaining Murraya species being retained in Murraya. This division of Murraya seems valid and will probably become increasingly accepted.

The type species, M. paniculata, is the well known ‘Orange jessamine’ or ‘Hawaiian mock orange’ (among other


 


 

names) that is sometimes cultivated as an ornamental in locales with a suitable cli- mate. The fl owers are large and fragrant, the fruits small and attractive, and the overall appearance pleasing. The distinctive vari- ety M. paniculata var. ovatifoliolata is sometimes cultivated as well, but is decid- edly less common. There are various horti- cultural selections of M. paniculata, and there are obviously wild ones as well.

There is some confusion with the status of M. exotica vis-à -vis M. paniculata. Swingle (1943) lists M. exotica as a syn- onym of M. paniculata. Huang (1959) con- siders this a variety (M. paniculata var. exotica). Stone (1985c) and Jones (1995) list

M. exotica as a separate species, although Stone (1985c) states ‘There is merit in Huang’s proposal for subspecifi c status but at least equal merit in regarding them as species.’ Huang later elevated them to species status (see discussion and citation in Kong et al., 1986), so perhaps lacking a defi nitive treatment M. exotica should be considered a provisional species.

The main differences are the larger, more ovate and acuminate leaves and larger fl owers of M. paniculata (Stone, 1985c). Thus, M. exotica would apparently become synonymous with Swingle’s (1943) M. pan- iculata, while M. paniculata in the sense of Stone (1985c) and Jones (1995) would apparently become synonymous with the






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