Japanese Maple Plant: Classification, Distribution, Characteristics and Diseases
Introduction
Japanese maple, or Acer palmatum, is a tiny, fine-textured tree that is indigenous to the understory of forests on the islands of Japan and neighbouring areas. In terms of landscape use, it has endured and frequently thrived in a variety of environmental circumstances. Japanese maple is a favourite of the nursery and landscape industries due to its capacity to adapt to its environment and its species’ intrinsic propensity for variation among seedlings (any mass of seedlings is certain to create any number of evident genotypic variants) (Mulloy, 1976). Approximately 120 species of maple trees and shrubs belong to the genus Acer. Maples are widely seen in residential and commercial landscapes, parks, and other public areas because they provide a wide range of options for size, growth habits, leaf form, and stunning fall colour. Numerous species are indigenous to Asia, including the well-known Japanese maple (A. palmatum). But some of the most widely cultivated species, like the red maple (Acer rubrum), silver maple (Acer saccharinum), and sugar maple (Acer saccharum), are indigenous to North America.
Japanese maples are very tolerant of climate and soil variations. Acer palmatum and its natural variations have adapted to a variety of settings on the islands of Japan in their natural habitats. These plants can be found all across North America, from upstate New York down the Atlantic coast to the southeastern states and across the Midwest, in soil types and climates ranging from the rain-forest type of the Pacific Northwest to the relatively warm environment of southern California. They flourish throughout Europe, including in the warm, Mediterranean climate of Italy, the nearly pure peat soils of the Netherlands’ Boskoop, and the diverse soils of Great Britain.
Classification
Kingdom: Plantae
Order: Sapindales
Family: Sapindaceae
Genus: Acer
Species palmatum
Scientific name: Acer palmatum
Common name: Japanese maple, Palmate maple, or Smooth Japanese maple
Distribution
Some believe the Acer palmatum complex to be widely dispersed, it has been noticed that populations of the plant thrive in Korea, China, and Taiwan and are closely similar to, if not identical to, those on the Japanese islands (Chang, 1990). Any of the 23 species of the genus Acer that are indigenous to Japan’s islands and neighbouring regions are generally referred to as Japanese maples. It’s fascinating to note that Acer palmatum and all of its variants are virtually unique to Japan, a little island around the size of Montana (Vertrees, 2001).
Characteristics
1. A. palmatum is commonly referred to in Japanese as Momiji, which roughly translates to “the baby’s hand” (Mulloy, 1976).
2. The famous little deciduous tree in Japanese gardens is Acer palmatum. It is one of the finest, most lovely tiny trees for texture, form, leaves, and autumn colour. It is delicate and refined.
3. Their compact stature, which ranges from shrub size to 8 metres (25 feet), makes them ideal for gardens and lawns with little space (aged, wealthy folks along the East Coast have reached maturation at 13 to 15 metres (40 to 50 feet) (Dirr 1998).
4. The growth habit varies and might be erect, rounded, horizontal, or weeping.
5. Depending on the cultivar, the foliage leaves are arranged in an opposing pattern and have emerging leaves that are green, bronzed, red, or purple. Each of the 5 to 11 (typically 7) lobes are slender, serrated, and has a pointy end.
6. The palmate venation is noticeable.
7. The fruits, which are two samaras per stalk with incurved wings and hang in pendulous clusters from the stems, are usually scarlet by June and July and turn reddish-brown in October, however by this time they are frequently sparsely borne or have absorbed.
8. The specimen can be single-trunked and branching, grafted onto a single-trunked standard, or multitrunked. Twigs can be green, brown, red, or purplish depending on the cultivar.
9. Bark can be green when young for green-foliaged types, brown when red-foliaged types, and eventually turn brown-grey for all types.
10. Almost everyone like the generally crimson hue, palmate form, or occasionally finely chopped (“dissected”) leaves. Acer species are more popular because of their consistent fall colour, which includes the reds, oranges, and yellows that are characteristic of most Acer species. This is in addition to their appealing form. More sophisticated and nuanced tastes value the Japanese maple’s gorgeous branch architecture, spring blossoms, and decorative fall seed set in addition to these evident qualities.
11. The prevalence of Japanese maple in artificial settings where people are most likely to be found may contribute to its popularity.
12. The Japanese maple tree is not large enough to prevent casual scrutiny or, on the other hand, minutely fine enough that only a skilled horticulturist with a hand lens could appreciate it.
Diseases
Japanese Maples are known to be susceptible to Verticillium, Fusarium, Botrytis, Pythium, Pseudomonas, and Anthracnose fungal diseases. All deteriorated plant tissue, particularly vascular tissue, impairs normal plant function and frequently causes whole or partial plant death. The bulk growing of seedlings or asexual cuttings is the main cause of fungal illness (Vertrees, 2001).
Numerous types of woody plants are known to be afflicted by the soil-borne disease verticillium. Young twigs will typically wilt and die back, which are ambiguous signs that resemble leaf blight, leaf scorch, and general root disturbance. Because propagation instruments frequently spread verticillium, careful sterilising is crucial. Two fungi known as botrytis and fusarium are known to infect large groups of seedlings and cause “damping off.” Both diseases also target more mature plants.
At or below ground level, Pythium and Pseudomonas damage budding seedlings, entering fresh tissue. The most frequent causes of Pythium and Pseudomonas losses are warm, humid springs and summers, with seedlings developing in alkaline to neutral pH conditions, particularly if the soil is thick or abnormally rich in nitrogen. Anthracnose is a disease that overwinters on dead branches and twigs and infects freshly growing leaves in the spring.
Anthracnose
Anthracnose is a typical fungus condition that affects shade trees. It is frequently an aesthetic issue on maple and won’t result in any long-term issues. It occurs frequently after cool, damp spring weather. Although symptoms differ depending on the host and pathogen, they typically manifest as a typical lesion on leaves. A. Saccharum and A. rubrum are infrequently afflicted by anthracnose brought on by Discula campestris. Numerous susceptible and resistant cultivars of sugar maple are reported by researchers at Auburn University in Alabama.
Cankers
A canker is any necrosis of the cambial tissue in the trunk or stem. The majority of the time, cankers are fungal infections or, less frequently, bacterial infections that have entered through open wounds. The appearance of the bark or stem may be abnormal due to cankers. There may be sunken, elevated, discoloured, etc., infected regions. There are visible signs of necrotic cambial tissue. Canker is a general term that refers to many distinct types of plant infections whose symptoms and degrees of reaction severity vary widely. Some cankers are completely thwarted by a plant’s defences, while others may be so severe that no healthy part of the plant is left and death occurs in a matter of years.
Japanese maples have been observed to be infected by fungi from the genera Nectria and Phytophthora, the latter of which is more frequently recognised as a root rot (Vertrees, 2001). At a Connecticut nursery, the pathogen responsible for high rates of mortality in Japanese maple asexual cuttings was found to be the fungus Colletotrichum acutatum. As the main pathogen of woody plants in North America, C. acutatum has not previously been recognised, therefore this is significant (Smith, 1993).
Chlorosis
Chlorosis, which is the gradual yellowing of a plant’s leaves, is a sign of nutritional insufficiency and is frequently brought on by an excessively acidic or, more frequently, an excessively alkaline soil pH. There are specific soil pH levels where macro- and micronutrients can be absorbed by roots. Nutrients become chemically locked up in the soil outside of these ranges and are no longer available for absorption. Chlorosis does occasionally happen even though Japanese maples are considered to be highly tolerant of different soil pH levels. Iron availability is restricted by an abundance of calcium in higher pH soils, and this iron deficit causes interveinal chlorosis. The effects of attempts to address the deficiency of iron are only transient (Vertrees, 2001). Before planting the tree, it is crucial to understand how the soil is at the planting location.
Leaf Scorch
Contrary to bacterial leaf scorch, the xylem-restricting wilt pathogen, physiological leaf scorch is a water relations issue. The necrosis of leaf tips and edges that extends inside between the veins is known as leaf scorch. The problem arises when plant roots cannot absorb enough water to counteract transpirational losses. Stem dieback results from extended dry spells. Heavy winds, salty winds, and unfavourable soil conditions, such as a heavy texture and poor permeability, or a sandy texture and low moisture retention, can all cause leaf scorch. Due to the high levels of transpiration and evaporation caused by these circumstances, the problem is exacerbated by the roots’ insufficient water supply. Similar leaf and stem conditions are brought on by high soil nitrogen or alkalinity levels, late spring frosts, and these factors together. In hot, sunny weather (during the hottest part of the day), overhead irrigation can scorch leaves, especially on Japanese maple varieties with crimson, dissected leaves. Leaf scorch harm results in a loss of vitality during the current growing season. Avoiding leaf scorch is made possible by generous mulching of the root zone and additional watering during dry spells (Vertrees, 2001). NC State researchers saw leaf scorch caused by a pigment bleaching that started at the tips of lower leaves and moved up the plant. They also noticed a different kind of leaf scorch that did not bleach and was characterised by sporadic and widespread leaf necrosis. Healthy, non-stressed plants had leaf water potentials of -14 bars under greenhouse growing circumstances, contrasted to stressed plants, which had leaf water potentials of -30 bars (Moles and Raulston,1979).
Question: In which soil can Japanese maples grow?
Ans: Japanese maples prefer slightly acidic sandy loams with low to medium levels of organic matter (Vertrees, 2001). Dirr (1998) suggests moist, rich in organic matter, and well-drained soils. Poorly draining and highly alkaline soil are two types that should be avoided.
Japanese maples may survive heavier soils or sandier, infertile soils because of their shallow root systems, as long as they are mulched properly and attention is paid to keeping an even watering schedule. Mulching is strongly advised to aid in the establishment of new plants and act as a protection against dry periods and cold snaps (Vertrees, 2001).