Ulmaceae

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Ulmaceae

Description

Monoecious or dioecious (?), evergreen, deciduous or semideciduous shrubs or trees, (in Mal.) unarmed and often buttressed. Leaves simple, (in Mal.) alternately arranged, petioled, pinnately nerved or triplinerved at base, often asymmetrical at base, entire or variously serrate. Stipules caducous or rarely rather long persistent and completely enclosing the bud, extrapetiolar or intrapetiolar, basally attached or rarely peltately attached to the nodes, free or connate. Inflorescences 1 -many-flowered, ♂,♀, ♂♀, or ♂ ⚥ axillary, subterminal, or borne on leafless, older branchlets or on short, lateral, leafless new shoots, paniculate, racemose, thyrsoid, cymoid, or rarely capitate, bracteate; Flowers functionally ♂,♀, or ⚥. —♂ Flowers solitary or in condensed cymoid clusters along the rachis, sessile or short-pedicelled; Fruit a drupe or a samara, faintly angular or flat and winged. Seed mostly exalbuminous;

Distribution

Africa: present Argentina: present Asia-Tropical: Australasia:, New South Wales (New South Walespresent); Queensland (Queenslandpresent) Europe: present Galapagos Is: present North, Central, and South America: present Pacific:, Hawaiipresent Pacific Islands: present Scandinavia: present South of Sahara: present Tahiti: present continental Asia: present tropics, subtropics, and temperate regions: present
There are 15 genera, c. 200 spp., widely distributed in the tropics, subtropics, and temperate regions of Europe (as far north as 70°, Scandinavia), Africa (South of Sahara), continental Asia, Malesia, Australia (Queensland and New South Wales), Pacific Islands (as far as Tahiti; incl. also Hawaii and the Galapagos Is.), North, Central, and South America (as far south as 40°, Argentina). .

Ecology



The rootlets of species of at least some Parasponia spp. (possibly also of some Trema spp.) mostly possess nodules which are caused by Rhizobium infections, similarly as in Leguminosae.

The capacity for aerial nitrogen fixation makes them extra suitable, useful and desirable for pioneering on waste and eroded lands (A. D. L. AKKERMANS, in litt.).

The structure and position of the inflorescence and flowers, particularly the amount of pollen grains produced and the structure of the stigmas, and also the absence of nectary, seem to suggest that pollination is most likely affected by wind, though insects may not be ruled out altogether as possible agents for pollination.

Except for Ulmus, which produces a dry, flat, winged fruit, the other Malesian genera have various types of fleshy drupes which turn to bright yellow, orange, or deep-red in colour when ripe. These drupes are most probably dispersed by various species of frugivorous birds or arboreous mammals. Alternatively, at least in some species, e.g. Celtis philippensis var. wightii which is very common in coastal vegetation, fruit dispersal may be carried out by water currents. In Ulmus the winged fruits are easily dispersed by wind.

It should be noted here that there is a very high percentage of seed abortion in Malesian genera for reasons unknown. This is made good by the production of a great number of flowers and fruits, produced regularly throughout the year or at least twice a year. Except for Ulmus, the embryo is protected by a strong, hard and durable endocarp. In all genera endosperm is usually scanty or absent.

Anatomy

For general surveys also covering the older literature see ; ; ; .
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SWEITZER'S study (l.c.) is the most up-to-date survey of leaf and wood anatomy of the Ulmaceae. Although his extensive research materials included very few Malesian species his general conclusions are probably largely applicable to the Malesian species as well.

The wood anatomy is indicative of the mutual affinities of all Ulmaceous genera. Shared characters are: predominantly simple vessel perforations, short vessel members, alternate intervessel pits. Fibres with simple to slightly bordered slit-like pits. Parenchyma at least partly vasicentric. Genera of the tribe Ulmeae (in Malesia only represented by Ulmus lanceaefolia) have exclusively homocellular rays. In Celteae (in Malesia all other genera) at least part of the ray tissue is heterocellular.

The wood of Ulmus lanceaefolia differs from all species described in literature in lacking the ring porosity and the typical ulmiform arrangement of vessel clusters (original observation). Instead, its vessel distribution resembles the diffuse porous group of tropical Celtis species. In Celtis the very striking differences in vessel distribution between tropical and extratropical species are well documented (cf. SWEITZER, l.c.). Although from SWEITZER'S and other publications some quantitative and qualitative differences between Malesian genera of Celteae can be deduced, our knowledge is still based on too limited materials to allow conclusions on diagnostic and systematic implications.

The leaf anatomy of Ulmaceae at the same time supports its coherence as a family and provides an interesting diversity, of great potential diagnostic and systematic value. All Ulmaceae share the dorsiventral leaf architecture. The stomata are confined to the abaxial epidermis and are of the anomocytic type. The indumentum includes bulbous-based unicellular trichomes the walls of which are usually silicified. Mineral inclusions of calcium carbonate or silica in cystoliths (with or without pegs) are of common occurrence. The trichome-complement, presence or absence of mucilage cells, crystal complement, loose or compact structure of the spongy tissue, petiole and midrib vasculature show a considerable diversity. SWEITZER'S data and other reports from the literature do not yet allow a leaf anatomical characterization of the individual Malesian taxa, but preliminary studies are indicative that this will be possible if more material is studied.

The entire evidence from vegetative anatomy supports the traditional placement of Ulmaceae in Urticales. — P. BAAS.

Taxonomy

The family name Ulmaceae was first introduced and defined by MIRBEL in 1815, at which time it included only Celtis and Ulmus. LINK (1831) proposed splitting Ulmaceae into two separate families, l.c. Ulmaceae to include Ulmus and related genera, and Celtidaceae comprising Celtis and its allies, an opinion which was supported by GRUDZINSKAYA (1967). However, all contemporary taxonomists generally agree to regard Ulmaceae as a natural taxon closely related to Moraceae and Urticaceae and to include these families in the order Urticales. Any difference of opinion is usually restricted to the inclusion or exclusion of a few genera in the family. In the most recent treatise, HUTCHINSON (1967) divided the family into two tribes, namely the Ulmeae (flowers bisexual, fruit not drupaceous, embryo straight, cotyledons flat or longitudinally folded) to include: Holoptelea, Planera, Phyllostylon, and Ulmus, and the Celtideae (flowers unisexual or sometimes bisexual, fruit drupaceous, embryo curved, cotyledons mostly variously folded) comprising Ampelocera, Aphananthe, Celtis, Chaetacme, Gironniera, Hemiptelea, Lozanella, Mirandaceltis, Parasponia, Pteroceltis, Trema and Zelkova. This subdivision was supported by SWEITZER (1971) who studied the anatomy of leaf and wood. However, as has been mentioned under Embryology and Palynology, the embryo of Zelkova is straight, and the pollen (also of Ampelocera and Hemiptelea) belongs to the Ulmus-typc (see also ERDTMAN, 1956). Furthermore in many species of Celtis the flowers are bisexual, and in Ulmus lanceaefolia and U. parvifolia the flowers are either functionally male or female. This seems to indicate that the tribal subdivision as proposed by HUTCHINSON is not a clear cut case, but that Ulmaceae is a natural taxon. It should be noted further that the Mexican genus Mirandaceltis is in the present study regarded as congeneric with Aphananthe.

As for phylogenetic relationship, there seems to be two different opinions. BESSEY (1915) and THORNE (1968, 1973) placed Ulmaceae along with Moraceae and Urticaceae in the superorder Malviiflorae, and considered them as families having a very close affinity to or derived from the Malvales. On the other hand, authors such as HUTCHINSON (1967), CRONQUIST (1968), TAKHTAJAN (1969), SWEITZER (1971), etc., are of the opinion that Ulmaceae, Moraceae, and Urticaceae are closely allied to or have been derived from the Hamamelidales.

Cytology

From various published data it seems that the chromosome number in the Ulmeae (Holoptelea, Ulmus, and Zelkova) is n = 14 and 2n = 28, 42, and 56, though reports of n = 15 and 30 have been made on Ulmus americana. In the Celtideae the number seems to be less constant varying from n = 10, 2n = 20, 28, 40 in Celtis (9 spp.); n = 30, 2n = 84 in Chaetacme (2 spp.); to n = 10, 10 + B, 18, 20, and 80 in Trema (3 spp.). It may be noted here that as for chromosome number, Ulmaceae seems to be closely related to Moraceae where n = 12-16, 2n = 24, 26, 28, 42, 56, and 84, and to Urticaceae of which n = 14, 28 and 2n = 22, 24, 28, 52, and 84.

Uses


  1. Timber. Throughout the north temperate regions the tough, strong and durable wood with attractive appearance and excellent bending quality of many species of Celtis and Ulmus is extensively used for various purposes including shipbuilding, panelling, furniture, boxes, crates, veneers, etc. and that of Zelkova and Phyllostylon for making weaver's shuttles, scales, piano-keys, etc. In Central America timber of Chaetoptelea (= ?Ulmus) is used for railway sleepers, frames and wheels of vehicles. In Africa and India wood of Holoptelea is utilized for various building purposes. In Malesia and neighbouring countries except Aphananthe cuspidata, Celtis rigescens, C. hildebrandii, C. tetrandra, Gironniera nervosa, Ulmus lanceaefolia and a few others, the trees seldom reach timber size, and as a consequence very little is known about their usage. Of these species the timber is locally used for making planks in house-building and other light constructions. The soft wood of Trema and other species of Gironniera is used locally for making tea-chests and match-sticks, for firewood and charcoal.
  2. Bark. Due to the high content of mucilagenous substances, decoction of barks of Holoptelea, Parasponia, Trema and Ulmus mixed with some other ingredients is used in local folk medicines to cure ailments such as inflammation of mucous membrane, rheumatism, etc. The tough fiber is known to be used locally for making ropes.
  3. Root. Decoction of roots of Gironniera and Trema species mixed with other substances is used to cure sore mouth, diarrhoea, and also applied as protective medicine after child-birth.
  4. Leaves. Especially of Trema species leaves are used as fodder, though due to the presence of glucocides they could be poisonous if consumed in a large quantity.
  5. Fruits. In India fruits of Celtis and Holoptelea are known to be eaten.
  6. Shade trees. Trema has been used for shade in coffee and cocoa plantations in various parts of Asia.
  7. Soil conservation. In South Africa Trema has been planted to protect soils against erosion (SCHEEPERS c.s.). As both Trema and Parasponia species come up in dense serai stands on eruptiva, on fresh volcanic ash, are sometimes pioneers on lavastreams, and are almost invariably an important constituent of thickets, serai regrowths, and secondary forest, I would emphasize that they may represent an untapped cheap source for soil conservation for poor, eroded soils and old mining lands. They have all the favourable qualities of pioneer plants, indifference to soil, producing abundant seed, and that already at a very early age, and furthermore they are available almost throughout the year. Curiously I do not know of experiments by the Indonesian Forestry Service in this respect.

Phytochemo

SOLEREDER mentioned the more or less general occurrence of cystoliths and cystolith-like structures (SiO2 + CaCO3) in Ulmaceae. The tendency to accumulate carbonate of lime seems to be very strong in this family; CaCO3 is deposited in wall structures (e.g. hairs, cystoliths) and in cell lumina (e.g. in heartwood of Ulmus and Celtis; in seed coat cells of Celtis). Often oxalate of lime is also present in large amounts; solitary and clustered crystals occur in the family. Anatomically easily detectable internal excretion comprises also mucilage production. The mucilage is deposited in epidermal cells (many taxa) or in mucilage idioblasts in the meso-phyll of some genera and in barks and flowers of most species of Ulmus. The bark of Ulmus rubra MUHL. ('Slippery Elm') was used formerly as a mucilaginosum in official medicine. In mucilage-rich elm barks large mucilage idioblasts may develop to lysigenous mucilage cavities. Chemically elm bark mucilages are characterized by a high content of galacturonic acid, galactose, 3-0-methylgalactose and rhamnose. Ulmaceae are moderately strong accumulators of polyphenolic compounds. Derivatives of caffeic acid, catechins, pro-anthocyanidins (formerly leucoanthocyanidins), flavonols (especially glycosides of kaempferol and quercetin) and condensed (= flavanoid) tannins seem to occur more or less ubiquiteous in leaves, fruits, barks and woods. According to LEBRETON flavonoid constituents with a trihydroxylated B-ring (in casu myricetin and prodelphinidin), an assumedly primitive feature, are restricted to Celtideae. (H-)-Catechin was definitely identified in leaves, twigs and barks of European elms and its 7-xyloside was isolated from the stem-bark of Ulmus americana L. C-Glycoflavons (tremasperin) occur in leaves of Trema aspera Bl., and the wood of Zelkova serrata (THUNB.) MAKINO contains large amounts of the fungistatic 6-C-glucoflavonoids keyakinin and keyakinol. Tannin contents of woods, barks, leaves and fruits are moderate (mostly less than 10%). There is only one report in literature indicating a possible co-occurrence of galli- and ellagitannins with condensed tannins in Ulmaceae', bark and wood of Celtis australis L. contain gallic acid and derivatives of ellagic acid according to CHARI C.S. (1968).

Much chemical work was performed with elm barks and especially elm woods in connection with 'Dutch Elm Disease'. Cadinane-type oxigenated sesquiterpenes seem to be present in the young wood of every species. On aging (heartwood formation) or after fungal infection, synthesis and accumulation of fully aromatic (cadalenal, hydroxycadalenal) and (or) oquinonoid (the mansonones) cadinane derivatives take place in American elm species belonging to the sections Trichoptelea, Microptelea and Chaetoptelea; they seem to be absent from the sections Blepharo-carpus and Madocarpus in which all European elms are included. It deserves mentioning that the antifungal cadalenals and mansonones represent phytoalexin-like stress compounds in Ulmus, and occur at the same time as normal heartwood constituents in Ulmus and Zelkova (but not in Celtis); they are chemically identical with, or biochemically closely related to the gossypol-mansonone-group of constituents of many Malvaceae, Bombacaceae and Sterculiaceae (mansonones were first detected in the wood of Mansonia altissima A. CHEV.). It was recently shown that hemigossypol, the precursor of the long-known gossypol, is a phytoalexin in many malva-ceous plants and that p-quinonoid derivatives of hemigossypol are engaged in the plants resistance against attack by several phytophagous insects (). As far as ecological chemistry (defensive substances) is concerned, Ulmaceae much resemble members of the order Malvales. Leaf, bark and wood waxes were investigated by several authors in recent time. They seem to consist mainly of alkanes, long-chain fatty acids, wax alcohols and phytosterins. Additionally pentacyclic triterpenes are often present; P-amyrin (i), lupeol (ii), betulin (iii), friedelin (iv), friedelanol (v), moretenol (vi), simiarenol (vii) and simiarenon (viii) were reported from leaves and (or) barks of Celtis australis L. (iii), C laevigata WILLD. (vi), Holoptelea integrifolia PLANCH, (iv, v), Trema guineensis FICALHO (reported as T. orientalis Bl.; vii, viii), Ulmus americana L. (ii, esterified with cerotinic acid) and Zelkova serrata MAKINO (iv). The heartwood of Holoptelea integrifolia PLANCH, yielded 2α-hydroxy-3-epioleanolic acid (); this is the only triterpenic acid isolated hitherto from Ulmaceae. Seeds of Ulmaceae seem to store predominantly proteins and fatty oils. The oils have linolic (Celtis, Chaetacme, Trema), oleic (Holoptelea) or capric (Ulmus, Zelkova) acids as main fatty acid. Species of Celtis and Pteroceltis accumulate small amounts of quebrachitol in leaves; this cyclitol could not be detected in leaves of species of Ulmus and Zelkova (Hemiptelea included). Alkaloid-like compounds are recorded in literature from members of Ampelocera, Aphananthe, Celtis, Gironniera, Trema and Ulmus, but only in the case of Ampelocera ruizii KLOTZSCH an alkaloid-like compound isolated from leaves was chemically identified; it proved to be an α-pyridone derivative related to trigonelline (). The foetid smell of some Celtis woods of India, Indonesia Ckaju taV) and Africa is caused by skatol. Several species of Ulmaceae are reported to be toxic in literature. GRESHOFF isolated a toxic bitter principle from the leaves of Aphananthe aspera (THUNB.) PLANCH. (= Homoioceltis aspera Bl.) which he compared with his streblide (from Streblus asper LOUR.; strebloside is now known to be a cardenolide). Leaves of Trema cannabina LOUR. (= Sponia virgata PLANCH.) and of T aspera Bl. (= T. cannabina) were reported to be cyano-phoric; both species, however, are polymorphic with regard to cyanogenesis if the botanical identification of all plant samples investigated hitherto was correct. Leaves of T. aspera (= T. cannabina) contain another toxic principle called trematoxin; its chemical structure is not yet known.

From the taxonomic point of view three facts deserve special mentioning:
  1. Ulmaceae are generally included in Urticales; their chemistry agrees rather well with such a classification as is indicated by patterns of mineralisation and phenolic compounds.
  2. The chemistry of Ulmaceae resembles members of Malvales in several respects: chemistry of stress compounds; mucilages with high contents of galactose, rhamnose and galacturonic acid; some features of the poly-phenolic and triterpenic patterns.
  3. The classification of Ulmaceae in Ulmoideae and Celtidoideae () or Ulmeae and Celtideae () is not very satisfactory from the chemical point of view (see cadinane-type sesquiterpenes including mansonones and capric acid as main fatty acid in seed oils in Ulmus and Zelkova, but not in Celtis).


For more phytochemical details and references see — R. HEGNAUER.

Embryology

Apart from several species of Ulmus and Holoptelea very little is known about the sporogenesis and embryogenesis of the Ulmaceae. From a very limited information so far published it appears that the anthers are initially tetrasporangiate but become bisporangiate just before anthesis through the breakdown of the adjoining wall between the locules. The anther-wall development conforms with the so-called basic-type in which the parietal cells divide both anticlinally and periclinally to form the endothesium layer, two (Trema and Ulmus) or three to four (Holoptelea integrifolia) middle-layers and glandular tapetum. Simultaneous cytokinesis in the microspore mother-cells follows meiosis and as a result the pollen grains are initially arranged in either tetrahedral or decussate tetrads. At anthesis the pollen grains are either 2-celled (Holoptelea and Trema) or 3-celled (Ulmus). In Celtis, Holoptelea and Trema up to 80% of the pollen grains produced are sterile or imperfectly developed. The ovule is anatropous to hemianatropous, bitegmic, crassinucellar or tenuinucellar (in a few species of Ulmus) with the micropyle formed by both integuments (Celtis and Trema) or by the inner integument only (Holoptelea and Ulmus). In Holoptelea and Trema the megaspore mother-cell divides into 4 daughter cells arranged in a linear tetrad, and of these only the chalazal megaspore develops into Polygonum-type of embryo-sac. In Ulmus, however, the embryo-sac is tetrasporic and either belongs to Adoxa- or Drusa-typz or variation of these two types with 4-12 antipodal cells. The pollen tube enters the ovule either through the micropyle, the integuments or the chalaza. Endosperm formation is nuclear and the tissue is either diploid or triploid and later becomes cellular. Embryo development conforms with the Onagrad-type in Holoptelea and Solanad-type in Ulmus. Polyembryony is a common phenomenon, especially in Ulmus. The mature embryo is straight with broad, flat or planoconvex, equal or slightly unequal cotyledons in Holoptelea, Planera, Phyllostylon, Ulmus, and Zelkova, or curved with ascending hypocotyle and narrow, incurved or induplicate-plicate or variously folded cotyledons which are mostly unequal in length in Ampelocera, Aphananthe, Celtis, Gironniera, Parasponia, Pteroceltis and Trema.