Wisconsin Horticulture
Abutilon megapotamicum was formerly known as Abutilon vexillarium.
Abutilon megapotamicum
(aka: Callianthe megapotamica) Hailing from the hot bed of great garden plants. the semi-tropical/warm temperate region of southern Brazil and surrounding Uruguay and Argentina comes Brazilian bellflower. Abutilon megapotamicum is a fun and easy-to-grow hummingbird magnet for the perennial border. In the garden or in a hanging basket, Abutilon megapotamicum spreads to several feet wide in a single season. In the wild, Abutilon megapotamicum reaches 8′ tall, but in temperate climate gardens, it rarely exceeds 6′ tall x 10′ wide, and less when grown as a container plant. From late summer until frost, the plants are laden with cool 2″ hanging, lantern-like flowers composed of red calyces above the yellow petals, ending with its bright red privates dangling beneath. all carefully arranged between the thumb-sized green leaves. How about a hot Brazilian for your garden?
Maintenance:
The deciduous stems usually resprout in spring, unless winter temperatures drop below 10 degrees F.If so, flowering maples will generally resprout from somewhere below ground to slightly above the soil level. If your plant grows too large, you can cut it back all the way to the ground if you’d like and it will quickly resprout. About the only time, we don’t recommend cutting abutilon to the ground is in fall or winter. The ideal time to prune would be just prior to bud break in spring.
There will often be very little dieback of stems during mild winters, in which case little to no pruning is necessary come spring. Indeed it will often flower all winter in a sheltered location in winter.
Growing Conditions:
While A. megapotamicum is quite tolerant of dry soils, it really explodes in evenly moist, rich, compost-enhanced soils. While flowering maple flowers well in spring in shade, the summer flowers are a bit sparse. When grown in full sun, the floral density all summer and fall is quite amazing.
Natural Impacts:
Bees, butterflies, and hummingbirds are all regular visitors to flowering maple plants.
Nomenclature:
Abutilon megapotamicum was formerly known as Abutilon vexillarium.
Flowering Maple, Abutilon spp.
Flowering maples are a group of tender, evergreen perennials often used as seasonal annuals or houseplants in the Midwest. Sometimes also collectively referred to as Chinese bellflower or Chinese lantern – or just abutilon, flowering maples were popular during the Victorian era, later fell out of favor in the gardening world, but have returned to modern gardens in a plethora of forms. 
The genus Abutilon is a large group of flowering plants in the mallow family (Malvaceae) with over 200 species occurring throughout the tropics and subtropics. They range in height from 18 inches to 10 feet, and may be herbaceous perennials, shrubs, or small trees. The plants used as ornamentals are often A. x hybridum, a group of hybrids between A. darwinii and A. striatum, or cultivars of other species, such as A. megapotamicum and A. pictum. These plants get part of their common name from the resemblance of the foliage to maple leaves. The plants are unrelated to maples (Acer spp.) but do have palmate leaves often with deep, pointed lobes and/or serrated edges. The leaves may cause mild dermatitis in susceptible individuals. 
They are upright, branching plants—often with brittle stems—and some varieties have a structure reminiscent of a Japanese maple. They are low growing woody subshrubs that acts as herbaceous perennials in colder climates, supposedly hardy only in zones 9-11, but will survive in some colder areas as long as the plants have excellent soil drainage.
The generally solitary pendent flowers are borne on long pedicels from leaf axils or near the branch tips on the current season’s growth. The lantern-like buds open to cup- or bell-shaped flowers up to 3 inches in diameter. 
All have a calyx and corolla with 5 parts, with overlapping papery petals fused at the base, opening to various degrees from trumpet shaped to nearly flat. The flowers have staminal columns typical of the mallow family, with multiple stamens fused into a column lined with anthers, and a branched style with head-like stigmas inside the tube (very similar to that of its relative the hibiscus). The species generally have yellow or orange flowers, but others have red or pink petals with a darker center. 
Many are attractive to butterflies and hummingbirds. Hybrids rarely set fruit, but the species produce hemispherical pods (schizocarps) with multiple segments, each containing a few seeds. 
The species tend to bloom most prolifically in summer and fall, but modern hybrids have been developed to bloom nearly year-round. Flower color has been expanded by breeders as well, with flower colors ranging from white to reds, yellow, orange, coral and bicolors. 
Flowering maples are a great addition to annual or mixed beds or borders, The can be used alone or with other plants in containers, such as patio pots or window boxes. They work well in hanging baskets, where it is easier to see the downward facing flowers. Flowering maple can be grown as a multi-stemmed shrub or pruned as a standard for a more tree-like effect, and many types can even be used for espalier. The variegated forms may be grown more as foliage plants than for their flowers.
Grow flowering maple in full sun or partial shade. They grow in almost any type of soil as long as it is well-drained and evenly moist, doing best in rich soils. Plants will struggle if allowed to dry out too much. They typically do not have any significant insect or disease problems outdoors, but indoor plants are susceptible to the most common insect pests including aphids, mealybugs, scales and whiteflies, as well as spider mites. 
Flowering maples are easy to grow in containers and overwinter indoors. If given sufficient light, many will continue to bloom through the winter. They do best in a bright, sunny location, but prefer relatively cool temperatures (60’sF). Containers can be moved outdoors after the last frost, and should be moved back indoors before the first frost in the fall. Keep evenly moist during the growing season, but reduce watering indoors in the winter but avoid letting the plant dry out completely. Fertilize regularly starting in late winter when growth resumes, and stop in the fall. Some people recommend monthly fertilization, while others suggest every other week with half strength solution. Repot in the spring every year or two, using standard soilless potting medium. Moving to a larger pot will allow the plant to grow larger, so if space is limited just repot in the same size container. 
These plants have a tendency to become leggy and without regular pruning they can grow into a scraggly shrub. To maintain a dense, compact form they need to be pinched regularly. This will also promote more blooms as they only flower on new wood. Pinching, pruning and keeping a plant slightly root bound will help control its size. Major pruning should be done in early spring or late fall. Cut back branches selectively to shape the plant, making the cuts just above a node or on a strong, vigorous shoot near the plant’s base.
Abutilon species can be grown from seed (it may take a full year before they begin blooming), but cultivars and hybrids are propagated by softwood cuttings taken at any time of the year. Bottom heat will speed rooting. Tip cuttings can be taken in late summer to overwinter instead of keeping the entire plant.
Hundreds of varieties have been developed over the years. Some of the more commonly available abutilons include:
- ‘Bella’ series – blooms early with large flowers on compact plants (to 15 inches) in shades of apricot to orange, pink and deep red.
- ‘Bellvue’ Mix – blooms early with large flowers in vivid shades of red, orange and yellow
- ‘Canary Bird’ – sports yellow, trumpet-shaped flowers on rounded plants. It was awarded the Royal Horticulture Society’s Award of Garden Merit (RHS AGM) in 1993.
- ‘Kentish Belle’ – is more of a rambler with apricot-yellow flowers with purple stamens on compact plants.It was awarded the RHS AGM.
- ʻKirstenʼs Pink’ – has lots of soft pink flowers on a compact, upright plant (12-16”).
- A. megapotamicum, from southern Brazil and Uruguay, has small pendent flowers with yellow petals and a large red calyx. It was awarded the RHS AGM in 1993.
- A. × milleri has long, narrow leaves and pale orange flowers with red calyces. It was awarded the RHS AGM in 1993.
A. pictum has toothed leaves with 3, 5, or 7 lobes. The flowers are orange-yellow with dark red veins and protruding stamens. The cultivar ‘Thompsonii’ has yellow mottled leaves.- ‘Savitzii’ – has extensive cream marbled variegation on the green leaves, but few flowers with salmon-colored petals. It was awarded the RHS AGM in 1999.
- ‘Souvenir de Bonnʼ – has leaves with creamy white edges and soft peach-orange flowers, and will grow up to 3 feet tall. It was awarded the RHS AGM in 1993.