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The flowers of amur maple occur in oblong clusters circular in section about 1.5" long and 1" across on the tips of the branches; flower clusters don't appear until after the leaves have emerged. There are two kinds of flowers in each cluster, both yellowish white in color, about 1/8" across, both with five sepals and five petals (each 1.5-2 mm long); the petals' tips curve in over the central parts of the flower. One flower type is staminate with eight stamens (no ovary or style) within the ring of sepals and petals. The other flower type is "perfect" with both eight stamens tipped with light yellow anthers and with a distinct central style rising above the stamens that bears a split tip that curls back. Minnesota Wildflowers [https://www.minnesotawildflowers.info/tree/amur-maple] states that the style splits in two, but the amur maple present in Jackson Park has perfect flowers whose styles either split in two or split in three — both morphs are present in the same flower cluster. Fertilized perfect flowers produce a fruit that is a pair of winged seeds (samaras) joined seed-to-seed with the wings making an angle of less than 30° (much less than most maples). Initially green in color, the samaras develop reddish highlights before turning bright reddish pink in mid to late summer. When the fruit matures in early to mid-autumn, each samara is 1-1.5" long and turns light brown.

Acer

Acer ginnala

Amur maple [Blooms: Apr–May]

Norway maple produces separate male and female flowers, either on different trees or on the same tree. Flowers are produced in umbels of 10-30 flowers 2-3" across, either as the leaves are just unfolding or slightly before. Individual flowers are about 6-8 mm across; each has five 1/8" long sepals, five ~1/2" long petals, both of which are greenish yellow, and a brownish central disc. Male (pistillate) flowers have eight fertile stamens; female flowers have a green pistil with a pair of basal wings and a pair of styles, all surrounded by eight sterile stamens. Pollination occurs primarily by insects (bees). Fertilized female flowers produce pairs of winged fruits (samaras) joined at the seeds with an angle between the samaras of slightly less than 180°. The mature fruits are 1.5-2.5" long and turn brown in the autumn.

Acer

Acer platanoides

Norway maple [Blooms: Apr]

Silver maples may produce male flowers on separate trees from the female flowers or both male and female flowers may be produced by the same tree. Flowers emerge before the leaves. Staminate flowers occur in small (1/3" across) clusters on short, lateral spurs from the twigs. The staminate flowers are yellowish-green to red. Individual staminate florets consist of four sepals and 4-6 stamens; there are no petals. Pistillate florets also occur in small (1/3" across) clusters on short peduncles bordered by several scaly bractlets; the florets are greenish-yellow to red in color. Individual pistillate florets consist of four sepals and a pistil with a pair of styles; there are no petals. The female florets are wind pollinated. Fertilized pistillate florets produce a pair of conjoined winged fruits (samaras) at about 90° from each other; when mature, the samaras are light brown and 1.5-2.5" long, falling to the ground in early summer. Unlike most other maples, silver maples produce fruits (samaras) that can germinate in the spring of the year in which they are produced.

Acer

Acer saccharinum

silver maple [Blooms: Mar]

Sugar maple trees may produce male and female flowers on separate trees or may produce male and female flowers on the same tree, even on the same branch. Male flowers are produced in drooping umbels, with 3-4" long, hairy pedicels. Individual male flowers are about 1/8" long consisting of a yellowish-green calyx with five teeth and 6-8 stamens with yellow anthers (in young flowers) that extend well outside the boundary of the calyx; petals are absent. Female flowers are also produced in drooping umbels; they are 1-2" long (including the hairy pedicel), but the flower itself is only 1/8" long consisting of a yellowish-green calyx with five teeth, a two-celled ovary, and a divided style that extends beyond the margin of the calyx. Again, petals are absent. The female flowers are wind pollinated. Fertilized flowers produce pairs of winged fruit (samaras) each about 1" long, with the two fruits at a 60-90° angle to each other. The samaras mature over the fall and must be exposed to an extensive interval of sub-freezing temperatures during the winter in order to germinate.

Acer

Acer saccharum

sugar maple [Blooms: Apr–May]