Thunbergia, a Genus of Many Species
By Marie Harrison (can2grow)September 11, 2012
The bush clock vine, or king’s mantle (T. erecta), is a well-mannered shrub capable of growing 4 to 6 feet tall, though in my garden it stays about three feet tall. Cultural requirements are very similar to those of the blue clock vine. King’s mantle is easily recognized as a member of the Thunbergia genus with its yellow-throated tubular purple flowers, but the flowers and the leaves are smaller than its taller cousins. It has grown happily in my Zone 8b garden for many years, returning reliably from the roots every spring.
Another member of the genus is T. alata, a twining true vine having bright yellow, white, or orange flowers with five petals surrounding a brownish purple tubelike center. This tropical perennial grows about 8 feet tall and appreciates morning sun and afternoon shade. Although it is hardy in tropical areas, it is not even root hardy in my Zone 8b garden. However, it reseeds, and new plants spring up from these seeds every spring. Often they often wane with summer’s heat. Cultivars include ‘Alba’ (white), ‘Aurantiaca’ (yellowish orange), ‘Bakeri’ (white), and ‘Susy’ (mixed).
Very similar to T. alata is T. gregori (syn. T. gibsonii), commonly called orange clock vine. A tender perennial hardy to 25°F (Zones 9-10), this native of Africa bears bright orange flowers that lack the dark centered eye of its cousin. Quick-growing vines climb 8 to 10 feet tall and bloom from mid summer to late fall. Plants can be grown cascading from hanging baskets, climbing a chain link fence or other structure, or as a vigorous groundcover.
The vigorous Thunbergia grandiflora, called blue sky vine, sky flower, clock vine, or sky vine, is capable of covering large trellises or arbors. In summer it blooms freely with sky blue or white morning glory-like flowers. Various sources rate it as root hardy to Zone 8b, but I have lost this plant during winter freezes. I do not depend on it to return from the roots each spring like the slightly more cold-tolerant T. erecta and T. battiscombei. In tropical areas, the plant may spread in places where it is not wanted. In Queensland, Australia, and some other tropical areas, it is an exotic invasive plant. Because it has naturalized in some parts of South Florida, the University of Florida IFAS Assessment of Non-Native Plants in Florida’s Natural Areas advises caution for south and central Florida.
Thunbergia mysorensis is a vigorous vine growing 10 to 20 feet tall or more that is hardy only in tropical areas. Large and dramatic dangling string-like flower spikes up to a yard long hang on the plants from spring through fall. The flowers are a bicolor combination of bright yellow insides with reddish brown or burgundy sepals that color the outside. Gardeners use it to climb a high pergola or other sturdy structure where its pendulous clusters of slipper-shaped flowers can hang down and be within easy view. Descriptive common names include brick and butter flowers, lady slippers vine, and dolls’ shoes.
Another member of the genus is Thunbergia coccinea, or red clock vine. Rare in cultivation, it blooms from late fall through winter and wanes during the summer season. Terminal clusters of tubular scarlet flowers hang from down and are best seen trailing down from a support.
Other species of Thunbergia can be found in the literature but seem much less common in gardens. T. elegans, T. ikbaliana, T. lutea, T. wrightiana, and T. vogeliana are listed by the GRIN website.
Whichever genus you choose, this group of plants offers many choices for gardeners. Most are not hardy beyond Zones 8 or 9, but they can be grown as annuals for a one-season show or planted in containers and moved to protected places in the winter. These beautiful plants with varied colors and growing habits just might provide the finishing touch for your garden.
|Please mouse over pictures for picture credits to Kell, Htop, and Seedpicker_TX. All other pictures are by the author.|
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