palmatum – refers to the palmate nature of the leaves

• each leaf has several lobes (typically 5–7) that all originate from one point, looking like an open hand with outstretched fingers
• scientific name given by Swedish doctor-botanist Carl Peter Thunberg (student of Linneas), who traveled in Japan late in the eighteenth century

Native range: Korea, Japan

Leaves:

• 5–9 palmately lobed
• doubly serrate
• lobes:
  • deep (goes beyond middle of leaf—some way beyond)
  • oblong-lanceolate

Flowers:

• inflorescence – clusters (corymbs) w/ 6–20 flowers
• red or purple
• dioecious
• 5 sepals & petals
• 2 stamens & styles

Fruit:

• schizocarp – double samara
• divergent (90 degrees) wings
• somewhat persistent in winter
• no hairs

Other characteristics:

• small deciduous tree 10–25 ft. tall
• leaf color and degree of lobe depth high variable among the hundreds of cultivars

Relevant info:

• long cultivated in Japan
• introduced to and widely cultivated in China (according to Kew Royal Botanical Gardens and Flora of China)
• introduced into England in 1820 and available from a California nursery by 1854
• at least 350 cultivars are used in Europe and North America
• 23 species of Acer are native to Japan and the common name ‘Japanese maple’ may refer to any one of them
• often used in bonsai
• centuries-old Japanese names include kaede (maple) and momiji (autumn colors and maple)

Ecology & Adaptations:

• native to Japan & Korea
• found in shady temperate woodlands as understory tree
• pollinated by bees, hoverflies, and wind
• sexual reproduction – heterodichogamous sexual system:
  • protandrous – pollen is shed before stigmas are receptive
  • protogynous – stigmas are receptive before pollen is shed
  • maximizes the chances of cross-fertilization among individuals and genetic diversity in the population
• seed dispersal by wind aided by ‘wings’ of samara
• small rodents may further disperse seeds
• shade tolerant – low light-saturation point and photosynthetic rate
• herbivore & microbial pathogen defense:
  • low mesophyll porosity and higher trichome (appendages covered with villi) density (than leaves in full sun) increase leaf toughness
  • mutualism with mites:
    • plant secretes small amount of nectar from the distal vein at the leaf margin
    • nectar attracts mites that live in pocket-and-tuft type of domatia (specialized structures on the undersides of leaves) and protect leaves from pathogenic fungi and small herbivorous arthropods
• wildlife – seeds eaten by wood mice