One of the showier species of ash in terms of floral display, Fraxinus sieboldiana is native to southeastern China, Korea, and Japan. The plant in today’s photograph was grown from seed collected in Japan two decades ago.
Siebold’s ash is a forest inhabitant, growing on moist wooded slopes and along forest streams. Photographs of it in habitat can be seen via Cédric Basset’s Asian Flora: Fraxinus sieboldiana. References vary on reported heights: Flora of China reports growth to 8m (25 ft.) while the International Dendrological Society’s Trees and Shrubs Online suggests twice that height.
References also disagree on the reproductive properties of these plants. Wikipedia claims (for Fraxinus in general):
Most Fraxinus species are dioecious, having male and female flowers on separate plants but gender in ash is expressed as a continuum between male and female individuals, dominated by unisexual trees. With age ash may change their sexual function from predominantly male and hermaphrodite towards femaleness
The Plants for a Future database suggests (inaccurately) that Fraxinus sieboldiana is dioecious (as evidenced by Eike’s photograph containing hermaphroditic/bisexual flowers, or flowers with both male and female parts). However, the Flora of China (linked above) claims that the flowers are polygamous (should probably have written that the plants are polygamous), which can either mean having male, female, and bisexual flowers on the same plant or with bisexual and at least one of male and female flowers on the same plant–better, but still nonspecific as to which particular reproductive system is used. A few references are precise, and assert that Fraxinus sieboldiana is androdioecious (additional reference). This means that individual plants either bear male flowers or bisexual flowers; note that if this is the case, then the plants are not polygamous as per Flora of China. I’ve not found a reference, but it is possible that with age plants of Siebold’s ash formerly bearing only male flowers begin to additionally produce bisexual flowers–pollen is easy and cheap to produce, while seeds and fruit require more energy and nutrient investment (better tolerated by mature trees, generally). In summary, if individual plants either bear only male flowers or hermaphroditic flowers, then the species is androdioecious; if individual plants transition from bearing only male flowers to bearing both male and hermaphroditic flowers, then polygamous should be used to describe mature trees only.