Encephalartos ferox subsp. emersus Rousseau, Vorster & Van Wyk, 2015

Rousseau, Philip, Vorster, Pieter J., Afonso, Abilio V. & Van Wyk, Abraham E., 2015, Taxonomic notes on Encephalartos ferox (Cycadales: Zamiaceae), with the description of a new subspecies from Mozambique, Phytotaxa 204 (2), pp. 99-115 : 107-110

Encephalartos ferox subsp. emersus Rousseau, Vorster & Van Wyk , subsp. nov. ( Figs 4 , 5C , 6 , 7A, 7B , 8 & 9 )

Most similar to E. ferox subsp. ferox but distinguished (see Table 1) by its invariably emergent stems ( Fig. 4A ). Shorter unarmed section of the petiole ( Fig. 7A ), shorter leaves, narrower ( Fig. 8B ) and more closely spaced leaflets ( Fig. 5C ) present from the seedlings stage ( Fig. 9I ), with more leaflet pairs per leaf. Strobili and peduncles are smaller with a propensity for being yellow ( Fig. 4B , 6A, D, E ), while megasporophylls are discolourous, green internally when yellow externally ( Fig. 7A ). Vegetatively similar but reproductively dissimilar to E. hildebrandtii Braun & Bouché (1874: 18) from northern Tanzania and southern Kenya (ca. 2000 km to the north), which is distinguished vegetatively by arborescent stems (2.5–6 m), longer leaves (2–3 m), relatively narrower leaflets (80–350 × 13–45 mm), which are more dentate with up to nine marginal teeth, leaflets not undulating transversely, and the unarmed petiole shorter (10–70 mm).

Type:— MOZAMBIQUE. Inhambane: [precise locality withheld], growing on an annual floodplain close to a river on a raised sand mound, - 1 m, megastrobilus 26/04, Rousseau 1175 (holotype PRE, isotypes K, LMA, FTG, PRU [including liquid-preserved megasprophylls]).

Habit emergent with stems 500–1500 [716] mm long. Leaf length (960–)1335–2080 [1404] mm; unarmed section of petiole length (0–)10–43(65–125) [23] mm, number of spines (6–)8–12(–14). Median leaflets length × width × spacing: 100–165(–195) [145] mm × (20–)25–34 [29] mm × (15–)25–36(–42) [25] mm. Leaflet pairs 33–52 [41], veins 16– 20 (30–42) [24]. Microstrobili yellow, rarely orange, length 430–500 [340] mm, circumference 215–310 [257] mm; peduncle length 218–315 [249] mm; microsporophyll median height 25–32(–43) [26] mm. Megastrobili yellow, rarely red, length (285–)303–430(–480) [360] mm, circumference (507–)575–675(–729) [609] mm; peduncle length 60–135 [86] mm, peduncle circumference 125–157(–180) [139] mm; megasporophylls distinctly discolourous, yellow outside, green internally, median megasporophyll height 58–62 [57] mm. Seedling leaflet width 8–13 [10] mm.

Distribution and habitat:— This represents the most northerly distribution of the species, as fieldwork as far north as Baia de Sofala in Mozambique has not yielded any specimens. The subspecies is restricted to a single population consisting of two concentrations of individuals separated by ca. 1 km, although the habitat is homogeneous. It is separated from the nearest population of E. ferox subsp. ferox to the south by ca. 80 km and E. hildebrandtii to the north by ca. 2000 km. Encephalartos ferox subsp. emersus occurs in Vegetation type 44 ( Wild & Barbosa 1968), namely Deciduous Tree Savanna with Palms (badly drained lowland, Fig. 2 ). This vegetation type is found on poorly drained lowland, sublittoral zones as a result of water flowing from the undulation elevations of old quaternary dunes alternation with calcareous plains. Rainfall ca. 800 mm per annum. Outskirts are tree savanna dominated by Brachystegia spiciformis , and Pterocarpus angolensis de Candolle (1825: 419) amongst others. Floodplains are dominated by Phoenix reclinata Jacquin (1809: 27) , Hyphaene crinita Gaertner (1790: 13) , with pools and swamps interspersed, dominated by Phragmites communis Trinius (1822: 134) , Nymphaea nouchali Burman (1768: 120) , and Cyperus Linnaeus (1753: 44) species, while grasslands have irregular patches of several Paniceae and Andropogoneae grasses, with infrequent bare areas with Sarcocornia tegetaria Steffen, Mucina & Kadereit (2009: 453) . Encephalartos ferox subsp. emersus is restricted in this vegetation type to circular soil mounds ( Fig. 2A ) originating from giant termitaria (Complex 13 of Barbosa 1952) raised above the floodplain with its permanent ponds ( Fig. 2B ), with up to 20 individuals per mound. These mounds show clear successional vegetation patterns correlated with mound age and size starting with Phoenix reclinata and Hyphaene crinita , later including species such as a member of maculate Aloe Linnaeus (1753: 319) , Erythrina humeana Sprengel (1826: 243) , and finally large trees such as species of Euclea Linnaeus (1774: 747) and some of the adjacent savanna elements ( Fig. 2B ). Elevation -10– 8 m with the soils grey and sandy.

Literature citation:— Rousseau & Mann (2012).

Iconography citation:— Rousseau & Mann (2012: 25): figures 18 – 23.

Taxonomic notes:— See Table 1. In the diagnosis above, E. ferox subsp. emersus is also compared with E. hildebrandtii . This may raise the question whether our new taxon should not rather have been described as an infraspecific taxon of E. hildebrandtii . Is it not perhaps of hybrid origin, maybe even an allopolyploid involving E. ferox and E. hildebrandtii? Subsp. emersus is located about 2000 km south from the nearest known populations of E. hildebrandtii , thus genetic exchange between populations of E. ferox and E. hildebrandtii is highly unlikely, at least in relatively recent evolutionary times. This is supported as molecular evidence place E. ferox and E. hildebrandtii in different lineages ( Treutlein et al. 2005, Rousseau 2012). Encephalartos ferox . subsp. ferox has proved very difficult to hybridise with other members of the genus (Vorster, unpublished data; though E. hildebrandtii has not been tested); we would suspect subsp. emersus to behave similarly. Hitherto polyploidy has not been reported in cycads ( Gorelick & Olson 2011), making an allopolyploid origin for subsp. emersus unlikely. The reasons for making the new taxon a subspecies of E. ferox is due to geographic proximity, and the considerable similarity in leaflet and cone morphology. Moreover, the red cones rarely encountered in subsp. emersus would support a close phylogenetic association with E. ferox and not E. hildebrandtii . We mainly make mention of the vegetative similarity with E. hildebrandtii to aid in ex situ identification where geographic data are absent.

Phenology:— Strobili found dehiscent/receptive as early as (day/month): 28/02, 02/03, 13/03 with most strobili still immature, to 12/04 with most of the colony mature, to as late as 27/04 where most of the microstrobili are spent. Seed dehiscence is still to be observed but speculated to be around September based on circumstantial evidence and interviews with local people.

Fauna: —Two species of Coleoptera are associated with strobili during pollen shedding and are consistent with other pollinators of Encephalartos namely Porthetes sp. and a species of Erotylidae . Relationship with those found on E. ferox subsp. ferox has yet to be established. Damaged leaflets would also suggest the presence of Lepidoptera known to be associated with the genus. Seed coats are routinely eaten, most probably by birds and small mammals as is the case in the rest of the genus. Dispersal is very poor with many seeds never leaving the parental crown and thick stands germinating under parents.

Etymology: —Subspecific epithet derived from the Latin emersus, meaning “standing above” or “raised up”, in reference to the emergent stems as well as the vegetated soil mounds raised above the surrounding floodplains on which the plants grow.

Additional specimens examined (paratypes): — MOZAMBIQUE. Type locality: Rousseau & Mann 29–32, Rousseau & Mann 34–47, Rousseau & Mann 50–55 (PRU), Rousseau 1130B (PRU), Rousseau 1175–1183 (PRU), Rousseau 1250–1256 (PRU).

Conservation status: — Subsp. emersus does not occur in a protected area and illegal collecting has increased over a three year survey period with some of the removed material traced back to the nearby town’s tourist lodges. Large mature individuals are removed and seem to perform poorly in cultivation. The population size is estimated at 15 individuals per mound, with 70 mounds in the area of occurrence equaling>1000 mature individuals. Area of occurrence is 0.13 km ², area of occupancy is 0.05886 km ². As the subspecies occurs in a single locality where any stochastic event can eradicate the entire subspecies, and continued pressure from illegal collection is probable, we suggest the IUCN Red List rank of Critically Endangered A4d + B1a,b(v) + B2a,b(v).

Figures

FIGURE 2. Encephalartos ferox subsp. emersus: habitat. A. Plants of subsp. emersus (in foreground) growing among the palm, Phoenix reclinata, on a raised mound (ancient termitarium); note surrounding low-lying floodplain with scattered raised mounds covered by woody vegetation. B. Floodplain with circular mounds covered by Phoenix reclinata and other woody plants, including our cycad. The permanently high water table is reflected by ponds (foreground) scattered throughout the area. Photographs: P. Rousseau (A), P.J. Vorster (B).

FIGURE 4. Encephalartos ferox subsp. emersus: female plant from which the herbarium material designated as type (Rousseau 1175) has been collected. A. Emergent plant habit; the distinctive trunk is ca. 1.5 m high. B. Megastrobilus; showing macromorphology. Scale bar = 60 mm. Photographs: P. Rousseau.

FIGURE 5. Encephalartos ferox: morphology of median leaflets. A. Subsp. ferox; from southernmost populations (= E. kosiensis). B. Subsp. ferox; from northernmost population. C. Subsp. emersus. Scale bar = 40 mm. Photographs: P. Rousseau (A), P.J. Vorster (B & C).

FIGURE 6. Encephalartos ferox subsp.emersus: variation in cone macromophology.A. Prevalent yellow microstrobilus, note successional maturation. B. Uncommon orange microstrobilus. C. Microsporophyll detail. D. Only instance of multiple megastrobili recorded. E. Prevalent yellow megastrobilus. F. Rare red megastrobilus. Scale bars: A = 80 mm, B & C = 10 mm, D = 40 mm, E = 90 mm, F = 100 mm. Vouchers: B = Rousseau & Mann 50, C = Rousseau 1130, D = Rousseau & Mann 39, E = Rousseau 1252, F = Rousseau 1250. Photographs: P. Rousseau (A–D), P.J. Vorster (E & F).

FIGURE 7. Encephalartos ferox: megasporophyll detail. A. Subsp. emersus; transverse section of megastrobilus with green internal tissue. B. Subsp. emersus; median megasporophyll outer surface detail. C. Subsp. ferox; transverse section of megastrobilus with red internal tissue. D. Subsp. ferox; median megasporophyll outer surface detail. Scale bars: A & C = 30 mm, B = 20 mm. Vouchers: A = Rousseau & Man 39, B = Rousseau 1252, C = Rousseau 1183B. Photographs: P. Rousseau.

FIGURE 8. Encephalartos ferox subsp. emersus: vegetative morphology. A. Leaf; proximal portion. B. Leaf; median portion. C. Leaf; distal portion. D. Median leaflet; abaxial surface, showing distinct parallel venation. E. Cataphylls; adaxial (left) and abaxial (right) views. Scale bar = 40 mm. Voucher: Rousseau 1175. Artist: Lesley Deysel.

FIGURE 9. Encephalartos ferox subsp. emersus: reproductive morphology. A. Partial microstrobilus and peduncle; note basal reduced and sterile microsporophylls. B. Microsporophyll; adaxial view. C. Microsporophyll; abaxial view. D. Microsporophyll; distal (front) view. E. Megasporophyll with ovules; abaxial view. F. Megasporophyll with ovules; adaxial view. G. Megasporophyll; distal (front) view. H. Seed kernel with sarcotesta removed. I. Seedling leaf. Scale bar = 20 mm. Voucher: Rousseau 1175. Artist: Lesley Deysel.