Background: Collections of a tall species of Aristea from the southern coastal mountains of South Africa, with hairless, reddish brown bracts, have been variously identified as Aristea bakeri Klatt or Aristea capitata (L.) Ker Gawl., but do not accord with either of these two or any other known species.
Objectives: To describe a new species in Aristea to accommodate material from the southern coastal mountains that cannot be included in any known species.
Method: Existing herbarium collections were studied and the relevant published literature consulted.
Results: The new species Aristea rufobracteata is described for collections of tall plants from the Langeberg, Outeniqua, Tsitsikamma and Baviaanskloof mountains. It has a mostly condensed inflorescence, reddish brown bracts and small capsules.
Conclusion: The new species increases our understanding of the diversity in Aristea in southern Africa.
In the course of a review of herbarium collections of Aristea Aiton, we identified specimens of tall plants with hairless, reddish brown inflorescence spathes and bracts from the Langeberg, Outeniqua, Tsitsikamma and Baviaanskloof mountains in South Africa as an undescribed species. These collections were identified as Aristea bakeri Klatt or Aristea capitata (L.) Ker Gawl. [or their synomyms Aristea confusa Goldblatt, Aristea major Andrews or Aristea thyrsiflora (D.Delaroche) N.E.Br.], following Weimarck (1940), who included several early collections of the taxon from the George and Knysna districts of the southern Western Cape in his circumscription of A. capitata. The name A. capitata is now reserved for the Western Cape species from the Cape Peninsula and nearby. We include these early collections and several more recent collections from the southern coastal mountains in the new species Aristea rufobracteata, naming it for the unusual dry, red-brown spathes.
The African and Madagascan genus Aristea, now with some 58 species (Goldblatt & Manning 2013), is the sole genus of the Iridaceae subfamily Aristeoideae Vines (Goldblatt & Manning 2008). Centred in western southern Africa, where it is both most diverse and species rich, the genus has some eight species in Madagascar and 11 in tropical Africa; of these, five are shared with southern Africa and one with Madagascar (Goldblatt & Manning 2013; Goldblatt, Phillipson & Manning 2013). Aristea rufobracteata is a member of subgenus Aristea section Racemosae Weim. This section, which is restricted to the winter rainfall zone of southern Africa (Goldblatt [2012] 2013), is recognised by its robust habit, minutely notched style and three winged, apically dehiscent capsules containing flattened, lamellate seeds.
Research method and design
|
|
We examined all relevant collections at the herbaria with significant collections of southern African plants, namely the Bolus Herbarium, University of Cape Town (BOL), Royal Botanic Gardens, Kew (K), the Compton Herbarium, South African National Biodiversity Institute, Cape Town (NBG), the Missouri Botanical Garden, Saint Louis (MO), the National Herbarium, South African National Biodiversity Institute, Pretoria (PRE) and the South African Museum Herbarium, South African National Biodiversity Institute, Cape Town (SAM) (acronyms after Holmgren, Holmgren and Barnett [1990]). We also reviewed the relevant literature and implemented our conclusions with a formal description of the new species.
Aristea rufobracteata Goldblatt & J.C.Manning, sp. nov. Type: SOUTH AFRICA, Western Cape: 3320 (Montagu): Grootvadersbos, throughout Boesmansbos Wilderness area, after fire, 500 m – 1000 m, (–DD), 16 Nov. 1988, Ruiters 44 (NBG, holo.; NBG, PRE, iso.).
Description
Evergreen, rhizomatous perennials, 0.8 m – 1 m high, solitary or growing in clumps. Stem: subterete, with suberect branches borne at lower fertile nodes; lateral flower clusters sessile; branches short, crowded. Leaves: several, linear, 7 mm – 14 mm wide, firm and fibrotic. Flower clusters: many, crowded, upper clusters mostly sessile but lower nodes with short to long branches; mostly with two to four flowers in each cluster; spathes and bracts rusty brown, 8 mm –10 mm long, thinner and somewhat translucent near edges, obtuse, glabrous, becoming slightly crinkled and torn with age. Flowers: subsessile, blue; tepals obovate, ± 15 mm long. Stamens: with filaments ± 4 mm long; anthers ± 4.5 mm long. Style: ± 7 mm long, minutely three-notched at apex. Capsules: oblong in outline, narrowly three winged, 11 mm – 14 mm long. Seeds: lamellate, kidney shaped, mostly two per locule, margins papillate. Flowering time: mainly November and December, sometimes in October (Figure 1).
|
FIGURE 1: Scan of the holotype of Aristea rufobracteata, Ruiters 44 (Compton Herbarium, South African National Biodiversity Institute, Cape Town). |
|
Distribution
Scattered along the southern coastal mountains of the Western and Eastern Cape, where it has been recorded from the Langeberg between Heidelberg and Riversdale, the Outeniqua Mountains above George, the Tsitsikamma mountains near Clarkson, and the Baviaanskloof Mountains at Loerie (Figure 2). The species occurs on stony sandstone slopes in fynbos, mainly at an altitude from 400 m a.s.l. to 600 m a.s.l., and flowers primarily after fire.
|
FIGURE 2: Map showing the geographic distribution of Aristea rufobracteata. |
|
Diagnosis
Aristea rufobracteata is broadly similar to A. capitata in its tall stature, often densely columnar flowering axis and relatively short capsules (11 mm – 14 mm long). The flowering stem is branched but the branches are usually fairly short (sometimes up to 150 mm long) and erect or suberect. The individual flower clusters are sessile or subsessile and the inflorescence spathes and floral bracts are rusty brown, thinner and slightly paler toward the margins; the spathes are usually obtuse but are sometimes more or less acute (Figure 3a).
|
FIGURE 3: Flower clusters of Aristea species, showing bract differences: (a) Aristea rufobracteata, based on the specimen from Ruiters 44 (NBG), showing rusty bracts with obtuse apices; (b) Aristea capitata, based on the specimen from Orchard 451 (NBG), showing translucen t bracts with dark keels and attenuate aristate apices. |
|
The reddish brown spathes and bracts differ substantially from those of A. capitata, which are pale and silvery translucent, with a dark brown central keel extending upwards as an attenuate, cusp-like tip (Figure 3b). Aristea capitata is centred on the Cape Peninsula, extending eastwards to the Riviersonderend Mountains and northwards to the Piketberg, thus some distance to the west of the nearest station for A. rufobracteata.
Most collections of A. bakeri have a rather open, panicle-like inflorescence with well-developed secondary and sometimes even tertiary branches, which are occasionally suberect. The rust-coloured bracts are usually minutely hairy to scabrid beneath and always have evident, narrow, semitransparent margins. Aristea bakeri extends from the Cape Peninsula in the west to Uitenhage in the east, thus overlapping considerably with A. rufobracteata in the eastern half of its range, and both have been recorded in the mountains above George.
Capsules are particularly important in distinguishing species of section Racemosae (Goldblatt & Manning 1997). Aristea rufobracteata has capsules 11 mm – 14 mm long, thus shorter than most collections of A. bakeri, in which they are typically 18 mm – 30 mm long. The seeds are lamellate and irregularly kidney shaped, with brown papillae along the margins, like those of A. bakeri and its allies, Aristea juncifolia Baker and Aristea racemosa Baker. The margins of the seeds in A. capitata are smooth. Plants illustrated under the name A. capitata in Curtis's Botanical Magazine (Ker Gawler 1802) are almost certainly A. rufobracteata.
The important taxonomic differences amongst the three species are summarised in Table 1.
TABLE 1: Comparison of important taxonomic differences amongst Aristea bakeri, Aristea capitata and Aristea rufobracteata. |
Conservation notes
Aristea rufobracteata is relatively widely distributed and occurs in several conservation areas. There are no immediate threats. Additional specimens seen
WESTERN CAPE.—3320 (Montagu): Grootvadersbos, lower slopes of mountains, (–DD), 3 Dec. 1958, G.J. Lewis 5233 (NBG). 3321 (Ladismith): Riversdale, between the Little Vet river and Kampsheberg, (–CC), [without date], Burchell 6879 (K); Corente River Farm, (–CC), Aug. 1909 [without day], Muir sub Galpin 5359 (PRE). 3322 (Oudtshoorn): Montagu Pass, south slopes (–CD), 4 Nov. 1928, Hutchinson 1213 (BOL, K); Montagu Pass, 2000 ft [600 m], (–CD), 4 Feb. 1951, Hodge 8541 (K); between Oudtshoorn and George, (–CD), 14 Nov. 1942, Chippindall s.n. (K, PRE); George, below the power station, (–CD), 5 Nov. 1928, J.B. Gillett 2096 (NBG); mountains north of George Town [George], (–CD), [without date], Burchell 6011 (K); slopes of Cradockberg, 1600 ft [490 m], (–CD), Nov. 1928 [without day], Fourcade 4095 (BOL, K); George, Tierkop, 1600 ft [490 m], (–DC), 11 Nov. 1976, Bond W653 (PRE); Knysna, Buffelsnek, 2000 ft [600 m], (–DC), Oct. 1923 [without day], Phillips 151 (BOL, PRE); Knysna, Van der Waltshoek, (–DC), 20 Oct. 1922, Keet 998 (PRE); Knysna, Spitskop, (–DC), 4 Nov. 1970, Geldenhuys 166 (PRE).
EASTERN CAPE.—3325 (Port Elizabeth): Humansdorp, Loerie Forest Reserve, (–CC), 29 Jan. 1934, W. Long 66 (NBG).
Michelle Smith prepared the digital map. Anthony Magee prepared the figures.
Competing interests
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.
Authors’ contributions
P.G. (Missouri Botanical Garden) and J.C.M. (South African National Biodiversity Institute) contributed equally in all parts of this article.
Goldblatt, P., [2012] 2013, ‘Aristea (Iridaceae: Aristeoideae), a subgeneric classification’, Novon 22, 415–417. http://dx.doi.org/10.3417/2011119
Goldblatt, P. & Manning, J.C., 1997, ‘New species of Aristea section Racemosae (Iridaceae) from the Cape Flora, South Africa’, Novon 7, 357–365. http://dx.doi.org/10.2307/3391764
Goldblatt, P. & Manning, J.C., 2008, The Iris family: Natural history and classification, Timber Press, Portland.
Goldblatt, P. & Manning, J.C., 2013, ‘Iridaceae. taxonomic notes on Aristea (Iridaceae: Aristeoideae) in tropical and eastern southern Africa’, Bothalia 43, 207–211.
Goldblatt, P., Phillipson, P.B. & Manning, J.C., 2013, ‘The new species Aristea farafangana (Iridaceae) from Madagascar, biogeographic notes on Aristea in Madagascar, and a revised key to the genus’, Adansonia 35, 47–53 [series no. 3]. http://dx.doi.org/10.5252/a2013n1a4
Holmgren, P.K., Holmgren, N.H. & Barnett, L.C., 1990, Index Herbariorum. Part. 1: The herbaria of the world, New York Botanical Garden, New York.
Ker Gawler, J., 1802, ‘Aristea capitata. Tallest aristea’, Curtis’s Botanical Magazine 17, t. 605.
Weimarck, H., 1940, ‘Monograph of the genus Aristea’, Acta Universitatis Lundensis 36, 1–140.
|