Thereianthus bulbiferus
Introduction
An attractive plant with moderately dense spikes of light to mid-blue flowers that blossom in abundance in burnt veld, which makes it difficult to miss. Due to ongoing threats this plant faces, the population continues to decline in the wild.
Description
Description
Thereianthus bulbiferus is a deciduous, cormous plant up to 200 mm high. The plant has a globose corm with coarse netted fibred tunics which are accumulated with age and form a short neck around the base of the stem. The stem is erect, flexed outward only above the sheath of the second leaf and is usually unbranched and can occasionally be found with a short branch from the upper leaf axil. The stem with distinct clusters of cormels (3–4 mm in diameter) growing in the axil of the lowest leaf. Cataphylls (reduced, small leaves) are often dry and papery with a reddish-brown colour. The plant has 4 leathery leaves, often twisted, with 3 distinct veins and the main vein not thick but slightly visible; usually dry at flowering.
The inflorescence is an erect, dense spike of 7 to 15 flowers. The flowers are patent (spreading), they are pale to mid-blue, the lower 3 tepals with a white median mark near the base. The perianth is radially symmetrical with a funnel-shaped, slightly curved tube, 7–9 mm long, which is exserted 2–5 mm beyond the bracts. Stamens are curved, with filaments slightly exserted from the tube; anthers are purple and mostly facing upwards, with lilac pollen. Ovary forms ovoid capsules which bear subglobose-angled, yellowish-brown seeds. Flowering time is in early summer (November to early December).
Conservation Status
Status
It is unfortunate that Thereianthus bulbiferus is listed as one of the threatened species, due to the ongoing habitat loss, fragmentation and degradation caused by farming and urban expansion. As a result, the species is assessed in the Red List of South African Plants as Endangered (EN) and its few remaining locations continue to decline. The Millennium Seed Bank Partnership in South Africa, particularly in the Western Cape, has conducted some conservation interventions and has collected the seeds of this threatened species at Riebeek Kasteel in 2020. The collection has been shipped to the Millennium Seed Bank at Kew, United Kingdom, to be banked for long term storage. This collection is new to the bank, meaning that it has never been collected before. The seeds will be kept safe in the bank in Kew until the Seed Bank at Kirstenbosch National Botanical Garden is developed and running, then half of this collection will be withdrawn to be banked in our own bank in South Africa.
Distribution and habitat
Distribution description
Thereianthus bulbiferus is endemic to the southwestern Western Cape. The plant is adapted to winter rainfall, summer drought and montane soils derived from quarzitic sandstone. The major habitats of this species include Swartland Shale Renosterveld, Swartland Silcrete Renosterveld and Swartland Alluvium Fynbos. The distribution stretches from Piketberg to Gouda and Paarl. It is said to be common in the Elandskloof Mountains as single-species communities on the lower, moister flats and on the slopes, where it is restricted to drainage lines, and grows alongside Thereianthus spicatus which grows on adjacent drier sites.
Derivation of name and historical aspects
History
The name Thereianthus means ‘summer flowers’ and is derived from the Greek words thereios, meaning ‘summer’, and anthos, meaning ‘flower’ Thereianthus is a genus of flowering plants in the family Iridaceae which was first described as a genus in 1941. The entire genus is endemic to the Western Cape Province in South Africa. Eleven species are currently recognized under this genus and all of them flower during the hot summer months, mostly November to January. Thereianthus is a sister genus to Micranthus, Pillansia, Watsonia, Cyanixia, Lapeirousia and Savannosiphon. Unlike other crocoid genera, these 7 plant sisters are characterised by their axillary corm which develops in the axillary bud and not in the internode. It is this feature that makes them belong to the Watsonieae tribe of the Crocoideae subfamily. Thereianthus bulbiferus is unique in the genus in producing a cluster of cormels in the axil of the lowermost leaf, hence its specific name meaning ‘bearing or carrying bulbs’ from bulbus, meaning ‘bulb’ and fero, ‘to bear, carry or bring’. Although this species had been collected before, it was confused with T. bracteolatus and T. spicatus and it was only in 2010, when Manning and Goldblatt were able to properly examine plants in the field, that they realised it was a distinct species, and described it in 2011.
Ecology
Ecology
Thereianthus bulbiferus is pollinated by monkey beetles, anthophorine bees or generalist pollinators because of its short-tubed flowers. This species flowers in summer, mostly in the hot summer months, and it is stimulated by fire. It blossoms up in abundance in the season after the veld has been cleared by burning. It is believed that its corms are eaten by porcupines and moles.
Uses
Use
Thereianthus bulbiferus is a beautiful plant, it would be useful in the landscaping industry as it flowers throughout the summer months and can make an attractive garden and pot plant. There are no known medicinal uses of this plant.
Growing Thereianthus bulbiferus
Grow
The success rate of growing this plant is not clear but because of the habitat it grows in; it is believed that it would need a very well-drained, acidic, sandy soil. Thereianthus bulbiferus can be grown from seeds and vegetatively. According to Graham Duncan, it would be best to grow this plant in deep pots in a sunny position and start watering in autumn and stop watering after flowering in early summer. To propagate from seed, sow the ripe seeds in autumn, in a well-drained, sandy soil mix, such as 2 parts sand and 1 part fine-milled bark. Cover them with a thin layer of fine-milled bark and keep the seedlings in the original container until the next season. To propagate vegetatively, plant the corm offsets extracted from their mother plant in autumn. Place them 3-4 cm deep with 6-8 cm spacing. Plant them in a container and use an acid, sandy growing medium such as 3 parts medium-grained river sand and 1 part fine acidic compost or finely milled acidic bark, and place them in a well-ventilated, sunny location. Soak them with water every 7 to 10 days during the growing period between autumn, winter, and spring.
References
- Goldblatt, P. & Manning, J.C. 2020. Iridaceae of southern Africa. Strelitzia 42. South African National Biodiversity Institute, Pretoria.
- Manning, J.C. & Goldbatt, P. 2011. Taxonomic revision of the genus Thereianthus (Iridaceae: Crocoideae). Bothalia 41(2):239-267.
- Pacific Bulb Society. Thereianthus. https://www.pacificbulbsociety.org/pbswiki/index.php/Thereianthus. Accessed 14/06/2022.
- Von Staden, L. & Raimondo, D. 2014. Thereianthus bulbiferus Goldblatt & J.C.Manning. National Assessment: Red List of South African Plants version 2020.1. http://redlist.sanbi.org/species.php?species=1546-12. Accessed 10/06/2022.
Credits
Naomi Mdayi
Millennium Seed Bank Partnership
July 2022
Acknowledgements: the author gives many thanks to Graham Duncan, for assisting with information on how to grow the plant and to Ndileka Jaxa, for assisting with sourcing the books and publications about the plant.
Plant Attributes:
Plant Type: Bulb
SA Distribution: Western Cape
Soil type: Sandy
Flowering season: Early Summer
PH: Acid
Flower colour: Blue
Aspect: Full Sun
Gardening skill: Average
Special Features:
Good potplant
Horticultural zones
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