Geography and distribution
Cylindrocline lorencei has only been recorded on Mauritius Island (one of the Mascarene Islands), before it became extinct in the wild. Furthermore, it has only ever been found at one locality: an area called Plaine Champagne in the Mauritian Black River Gorges National Park.
Cylindrocline lorencei in the Tropical Nursery at Kew
A treelet or small tree to 2 m tall, with a trunk to about 7.5 cm diameter at the base, Cylindrocline lorencei is sparsely to moderately well-branched above and densely leafy in terminal rosettes. The stems are at first densely covered in woolly hairs, but gradually become less hairy with age, and are conspicuously marked with scars of fallen leaves. The older leaves are retained when dead (at least in cultivated material where they are easily removed by hand but clearly do not fall).
The olive green leaves are in spirals, distinctly rosettiform (in the wild) or forming a very loose rosette towards branch apices or simply leafy upper stems (in cultivated material). The leaves are attached directly to the stem with no petiole (leaf stalk), or can have a short petiole of 10–15 mm long. The leaf blade is oblanceolate (has a rounded apex and tapering base) and is normally 120–180 mm long by 45–55 mm wide. The leaf blade is slightly discolorous and lighter beneath, with a uniform covering of fine hairs on the upper surface and a dense covering of fine, silky hairs beneath. The main leaf veins are yellowish-green above and beneath.
The inflorescence is terminal (borne at the end of a stem) but is rapidly overtopped by axillary vegetative growth (in cultivated material). There are one to few inflorescences per shoot per season. The peduncle (inflorescence stalk) is up to 14 cm long, with a basal section of about 5.5 cm below the first leaf-like bract, and is densely covered in woolly hairs.
The compound flowerhead (capitulum) contains two different types of flowers (known as florets). The marginal florets are female, 3 mm long and toothed, with a style that extends beyond the corolla. The disc florets are hermaphrodite, at first male, later becoming female, with purplish, tubular corollas of 3-4 mm long.
The achenes (or cypselas, small, dry, one-seeded fruits) which develop from the marginal florets are 3-edged with a broader flatter face outside, whilst those from the disc florets are cylindrical and about 8-ribbed. The achenes are 3–3.5 mm long and brownish.
Flowering generally occurs from December to January and in June in Mauritius, and from June to July in cultivation, but is somewhat variable.
Threats and conservation
In 1973, when U.S. botanist David H. Lorence collected the material used by A.J. Scott as the holotype, he noted that there was only one plant in the Plaine Champagne. Jean Yves Lesuoëf’s collection of achenes (fruits) in 1980 confirmed the continued existence of this plant. At this point the species could have been classed as Endangered. However, Wendy Strahm noted in 1996 that the plant had since died: the species at that point would be recorded as Extinct. The plant was considered Extinct in the wild in 1990 yet IUCN’s ‘1997 Red List’ unfortunately still recorded the species as Endangered, the authors apparently unaware of the demise of the plant!
Although a number of plants have been repatriated to Mauritius it still remains to be seen if these will survive in the Native Plant Propagation Centre at Curepipe and, if replanted in their original habitat, whether they will survive in the Plaine Champagne.
No known uses. This species has ornamental potential and would be a spectacular addition to the conservatory as the species is easily micropropagated. However, in order to become commercially available, the Government of Mauritius would have to first grant permission. Benefits should then be shared with the country of origin with part of the profits from its sale used to assist conservation projects in Mauritius.
Cylindrocline lorencei in the Tropical Nursery at Kew
Cylindrocline lorencei is a tender shrub, requiring a glasshouse for cultivation in the UK, with a minimum temperature of 8˚C. No supplementary lighting or humidity controls are necessary. At Kew it is grown in the temperate zone in the Tropical Nursery where relative humidity is ambient, and ventilation is provided by fans hung over the benches, as well as via roof vents. Temperatures can reach 28–30˚C in the summer but the plant benefits from cooler temperatures in the range of 10-20˚C. The irrigation water is treated by a reverse osmosis process, which neutralises pH and removes dissolved salts.
Good plant growth and health are achieved using well-drained multi-purpose compost, based on a loam/coir/perlite medium with added slow-release fertiliser. The soil is allowed to become almost dry between waterings, and water-logging is avoided. Feeding with a well balanced fertiliser (NPK) is carried out every fortnight. Under these conditions, C. lorencei flowers well in summer.
The plants are relatively pest-free, with occasional minimal occurrence of mealy bug. Mechanical pest control is used, as the plants are very sensitive to chemical foliar sprays and are scorched when chemical sprays are applied.
Propagation by seed has been unsuccessful at Kew, possibly due to a self-incompatibility problem. The seeds produced by selfed plants appear not to be viable. Propagation can be achieved by tissue culture or cuttings. Cuttings are difficult and slow to root, sometimes taking up to four months.
Successful apical cuttings can be taken in the spring when they are potted into equal parts of peat/perlite and placed in a cabinet on a heated bench with a minimum temperature of 20˚C. As soon as they have rooted, they are potted on into a loam/coir/perlite mix and transferred to a cooler zone. Tissue culture has proved to be the most efficient method to propagate this species. Plants are weaned into a coir/perlite (70:30) mix when they are 1–2 cm or more in size, and placed inside a closed propagator on a heated bench for one to two weeks.
This species at Kew
Cylindrocline lorencei is currently found in the temperate zones of the Tropical Nursery and in the Micropropagation Unit at Kew.
Pressed and dried specimens of C. lorencei are held in Kew's Herbarium, where they are made available to researchers by appointment.
Micropropagation of critically endangered species
While many critically endangered species can be propagated by standard horticultural means, some species present challenges for ex situ conservation. Kew’s Micropropagation Unit develops and applies conservation biotechnology methods for in vitro culture and cryostorage of these taxa. Endemic species from island biodiversity hotspots such as St Helena, Seychelles and Mauritius have been propagated and repatriated using these methods. For example, Cylindrocline lorencei (extinct in the wild) has been propagated by tissue culture in the laboratory.
Achenes (fruits) from the one remaining plant in Plaine Champagne (Mauritius), had been collected by Jean Yves Lesouëf in 1980. Germination tests in the Conservatoire Botanique National de Brest in 1994 and 1995 failed as the seeds seemed to be not viable. However, newly developed techniques to grow the embryos in vitro resulted in three clones which, when grown on, produced seeds in 2003. The fact that any live material was found in the achenes resulted from a series of staining experiments in Brest. Small clusters of live cells were found in very few seeds when extracted from the achenes, leading to the production of three clones. The Royal Botanic Gardens, Kew accession is a donation from 2001 by Conservatoire Botanique National de Brest from one of the clones.
In 2006, micropropagated plants in jars were repatriated, but unfortunately the plants failed to establish during the weaning process on Mauritius. In another attempt, in March 2007, 12 mature plants (about 60 cm tall) were repatriated by Kew's Carlos Magdalena. This repatriation was successful and a year later some were still growing at the Native Plant Propagation Centre at Curepipe, Mauritius. However, the climatic conditions at this nursery are not ideal for this species, as C. lorencei originally grew at a higher altitude than the lowland, and more tropical, Curepipe facility.
Currently arrangements are being made in the Republic of Mauritius to start restoration work in the original areas where this species grew so that plants propagated at Kew and at Brest Botanic Gardens can be reintroduced to the wild.