Malus trilobata
Malus trilobata, the Lebanese wild apple, also known as the erect crab apple, three-lobed apple or deer apple, is a species of apple in the rose family. It has a discontinuous range in the eastern Mediterranean, including Thrace, coastal Anatolia and the Levant, but almost always as a rare species. It bears edible fruits and has been noted for its medicinal properties. Due to its attractive shape, bloom and foliage along with its drought and frost tolerance, it has found increasing interest in gardening and landscaping. Some authorities place it in the segregate genus Eriolobus, as Eriolobus trilobatus, either alone or together with the closely related hawthorn-leaf apple from the central Mediterranean. The species is thought to be threatened and declining.
Taxonomy and evolution
Taxonomic history
The taxonomic history of Malus trilobata is complex, reflecting its unique morphology. The species was originally described by Jean Louis Marie Poiret as a kind of hawthorn, Crataegus trilobata, based on a specimen collected by Jacques Labillardière in Lebanon, in 1810. Since then, the species has also been placed within the genera Pyrus, as Pyrus trilobata DC. Prodr., Sorbus, as Sorbus trilobata Heynhold, Cormus, as Cormus trilobata Decne., and Malus, as well as in Eriolobus Roem., whereby the latter was variably considered to include only M. trilobata or also M. florentina. Many authorities have sought to emphasise the species' distinctiveness by assigning it to unique genera, sections or subsections. Today, two competing treatments prevail: under the one that is currently accepted by Plants of the World Online, it is considered to belong to Malus. Traditionally, many researchers have further classified the species within its own section, Eriolobus, but the validity of these subgroupings has been questioned more recently. Alternatively, some authorities and databases prefer to separate M. trilobata within its own genus Eriolobus, as Eriolobus ''trilobatus M.Roem.Both positions appear to be supported by research findings. M. trilobata resembles other Malus species in floral morphology, and it is similar to some Malus species in leaf shape. For these reasons, Kazimierz Browicz considered it to be most closely related to Malus doumeri and, to a lesser extent, to Macromeles tschonoskii, both of which are native to East Asia. On the other hand, M. trilobata differs in the grit cells in its fruits, which are more commonly associated with Pyrus, even though they also occur in some other Malus species. Furthermore, phytochemical studies have shown that, uniquely in Malus, trilobatin replaces phloridzin as the main phenolic compound of the leaves in M. trilobata, which may similarly be taken to indicate a need for separation.
Some researchers recognise two varieties: Eriolobus trilobatus var. trilobatus M.Roem., which occurs throughout the species' range, and Eriolobus trilobatus var. sorgerae'' Browicz, which is only found in Gömbe, Antalya Province, Turkey, and is distinguished by having much smaller leaves than the type variety. Current consensus, however, recognises no sudivisions.
Modern taxonomy and evolution
studies based on plastid and nuclear DNA indicate that Malus trilobata falls between other species normally classified as Malus, and it appears to be sister to M. florentina, with both species often, but not always, positioned together on a branch that also contains the North American species prairie crabapple, southern crabapple and sweet crabapple. In Liu et al., this branch, called Clade II, is shown to either be basal to the rest of Malus, in nuclear phylogenies, or to be sister to Pourthiaea and thus closer to other Maloideae such as Sorbus and Aronia than to Malus proper, in plastid phylogenies. This discordance between nuclear and plastid phylogenies, the authors proposed, could be due to incomplete lineage sorting, allopolyploidy, or hybridisation, all of which were important mechanisms underlying the evolution of the Maloideae. The authors proposed hybridisation as the most likely scenario, whereby the ancestor of Clade II hybridised with the ancestor of Pourthiaea, so that all its descendants, including M. trilobata, inherited PourthiaeaAccording to Liu et al., Malus originated in North America and East Asia, most likely in the middle Eocene, around 43.58 million years ago. Also according to this study, Clade II, the clade M. trilobata belongs to, originated in western North America and subsequently spread to Europe and western Asia in the late Eocene via the North Atlantic Land Bridge. The split between Malus trilobata and its sister M. florentina, the two representatives of this clade in western Eurasia, was estimated to have occurred already in the early Oligocene, 32.81 million years ago. Malus antiqua, a species with lobed leaves from the Pliocene of Europe, recovered in Romania, is considered to be ancestral to M. trilobata or M. florentina.
Description
Malus trilobata is a medium-sized deciduous tree. It initially assumes a narrow, upright habit with horizontal or ascending branching, but becomes more rounded with age. The species usually attains a mature size of or up to height by width. The leaves are deeply 3-lobed, with each lobe usually again divided into several pointed lobes, so that the leaf may almost appear palmate. In leaf shape, the species resembles certain species of maple as well as the chequer tree. The leaves are glossy and glabrous above, bright green and hairy below, especially on the veins. They are rather stiff and slightly wider ( than long (, turning from orange to red to deep purple in fall.The tree blooms relatively late — usually between May and June in the European part of its range — bearing large flowers with white petals and up to in diameter, with flowers appearing in loose umbels of up to 10. The apple fruits ripen in fall between October and November. They are roundish and large, being around in diameter and weighing around. Yellow in colour, they are edible and reportedly have a good taste. The pulp has grit cells, which is otherwise atypical of apples, but common in pears. The seeds are dark and around in diameter. The bark of the tree is dark grey, deeply fissured and scaly with age, and it develops a deep root system.
M. trilobata is diploid, with a chromosome number of 2n=34.
Distribution and ecology
Malus trilobata is distributed in mountainous terrain in the eastern Mediterranean, however, its range is remarkably disjunct, consisting of several disconnected populations. A general, albeit outdated distribution map of the species can be found in . In the European part of its range it has been recorded down to altitude, but it has also been observed at and on Şaphane Mountain and Mount Lebanon, respectively. M. trilobata is not endemic to Lebanon, despite claims to the contrary.In Europe, it is known from Thrace, specifically Evros Prefecture in Greece and the eastern Rhodopes in Bulgaria. Here, it occurs between in xero-thermophilous communities on acidic siliceous soil, together with deciduous oaks and Turkish pine, fellow Rosaceae, mock privet, Greek strawberry tree, Oriental hornbeam, flowering ash, terebinth, tanner's sumach, cade juniper, garland thorn , bladder-senna, black bryony, pink rock-rose , wild asparagus and traveller's joy .
In Anatolia, the species is distributed in the Aegean and Mediterranean regions, that is, the northwest, southwest, south and southeast of the peninsula. The largest populations exist in the Taurus Mountains between the Berit Daǧi and Amanus mountains. A sizeable population exists also in Antalya Province where, however, the species is reportedly not common either. In the vicinity of Antalya, it occurs on neutral and chalky as well as sandy soils in oak and pine forest communities between altitude alongside oaks, black pine, Rosaceae including common hawthorn, oleaster-leaved pear, dog rose and holy bramble, junipers, storax, Spanish broom, Balsamic sage, large-flowered lampwick, sowbread, yellow-spine thistle and smilax .Apparently the largest population persists in the Levant, especially in the Lebanon Mountains of Lebanon, which is also the type locality of the species. For example, a large population occurs in Horsh Ehden nature reserve. Nevertheless, the species is rare also in Lebanon: a comprehensive survey in 2018 identified a total of 55 localities, the lowest count among the 27 tree species surveyed, with the next lowest count being 92 for silver almond. In contrast, Aleppo oak and kermes oak, the two most frequently recorded species, where found at 2092 and 1914 locations, respectively. In Upper Galilee, M. trilobata is a component of mesophytic plant communities dominated by kermes oak, together with Syrian maple, buckthorn, hawthorns, bay laurel, ivy, butcher's broom and wild peony.
Throughout its range, M. trilobata is distributed mainly on rocky slopes and neutral and acidic soils. In the Mediterranean, the species is largely restricted to seaside slopes close to the sea, and ecological niche modelling conducted in Lebanon indicates that it requires cooler temperatures, ample rainfall and more than 20% cloud cover, suggesting that it is a Mediterranean mountain or temperate relict species. Of the local tree species, it is thus most similar to Cilician fir , Balkan maple , Lebanon cedar , flowering ash , Syrian juniper , Turkey oak , sessile oak , Quercus kotschyana, and chequer tree, and is no Mediterranean species in the strict sense. ''M. trilobata is insect-pollinated, and, like other Malus, is thought to be pollinated primarily by bees. M. trilobata bears large fruit that drop to the ground when ripe, and is most likely primarily consumed by mammals, including horses and deer, which is also reflected in autochthonous names, such as deer apple and horse apple. Research conducted in Horsh Ehden, Lebanon, indicated that M. trilobata saplings were strongly facilitated by the presence of mature prickly juniper individuals, as these reduced environmental stress, particularly if their canopy cover was reduced by dwarf mistletoe infestation, which can induce severe foliage loss. On the other hand, M. trilobata saplings were only recorded in forest gaps as opposed to the forest inside. M. trilobata is a host plant for Ropalopus ledereri, a species of longhorn beetle from the eastern Mediterranean that feeds on the thin terminal branches of Malus species, Crataegus'' species and kermes oak.