Bothalia 35,2 (2005)
FIG U R E 9 .— K now n distribution o f A. ormocarpoides.
Other specimens examined
L IM PO PO .— 2 4 2 9 (N ylstroom ): Z w e m k lo o f 2 83-K T , 9 0 9 m , ( - D B ) , 0 4 -0 3 -2 0 0 4 , T. Mukoma & P.J.H. Hurter 70 (PR E, PRU); Thornhill 5 4 4 K S , S ekw ati, 9 8 5 m . ( - D B ) , 0 4 -0 3 -2 0 0 4 , T. Mukoma & P.J.H. Hurter 71, 72 (PR E).
A C K N O W L E D G E M E N T S
We are indebted to Miss Robyn Luyt and Mr Tovowani Mukoma for technical assistance, Dr Hugh Glen for the Latin diagnosis, Sandie Burrows for the line drawing, and SABONET, the South African National Biodiversity Institute and the University o f Pretoria for financial sup port.
R E FE R EN C E S
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chloroplast D N A restriction site variation for system atics o f Acacia (Fabaceae: M im osoideae). Systematic Botany 25: 6 1 8 -6 3 2 . C O A TES PALG AVE, M. 2 0 0 2 . Keith Coates Palgrave Trees o f south
ern Africa, edn 3. Struik. C ape Town.
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H U R TER , P.J.H. & V A N W Y K , A .E . 20 0 4 a . A n ew sp e cie s o i Acacia (M im o so id ea e) from M pum alanga, South A frica. Bothalia 34: 4 2 —44.
H U R TER , P.J.H. & V A N W Y K , A .E . 2 0 0 4 b . A n ew sp e cie s o f Acacia (M im o so id ea e) from the p rovince o f L im pop o, South A frica. Bothalia 3>4: 1 0 9 -1 1 2 .
H U R T ER , P.J.H. & V A N W Y K , E. 2 0 0 1 . First distribution record for Brachystegia spiciformis (C aesa lp in io id ea e) in South A frica. Bothalia 31: 43.
L U CK O W , M ., M ILLER , J.T., M U RPH Y , D.J. & L IV SH U L T Z , T. 2 0 0 3 . A p h y lo g en etic analysis o f the M im o so id ea e (L eg u m i nosae) based on chloroplast D N A sequence data. In B .B . Klitgaard & A . Bruneau. Advances in Legume Systematics 10: 1 9 7 -2 2 0 . R oyal B otanic Gardens. Kew.
M ILLER, J.T. & BAYER, R.J. 2000. M olecular phylogenetics o f Acacia (Fabaceae: M im osoideae) based on the chloroplast tmKJmatK and nuclear histone H 3-D D N A sequences. In P.S. H erendeen & A. Bruneau, Advances in Legume Systematics 9: 1 8 0 -2 0 0 . London. M ILLER , J.T. & B A Y E R , R.J. 2 0 0 3 . M olecu lar p h y lo g en etics o f
Acacia subgenera Acacia and Aculeiferum (F a b a cea e: M im o so id ea e) based on the chloroplast matK co d in g seq uence and flanking tm K intron spacer regions. Australian Systematic Botany 16: 2 7 -3 3 .
PEDLEY, L. 1986. D erivation and dispersal o f Acacia (L eg u m in o sa e), w ith particular reference to A ustralia, and the recognition o f Senegalia and Racosperma. Botanical Journal o f the Linnean Society 92: 2 1 9 -2 5 4 .
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P.J.H. H U R T E R * t and A .E . V A N W Y K **
* L o w v eld N ational B otanical Garden. P.O. B o x 1024, 1200 N elspruit. t Student affiliation: Departm ent o f B otany. U niversity o f Pretoria. 0 0 0 2 Pretoria.
** H .G .W .J. S c h w e ic k e rd t H erbarium . D epartm ent o f B o ta n y , U niversity o f Pretoria, 0 0 0 2 Pretoria.
M S. received. 2 0 0 4 -0 8 -0 4 .
LAM IACEAE
PLECTRANTHUS PORCATUS, A N E W SPEC IE S E N D E M IC TO TH E S E K H U K H U N E L A N D C E N T R E O F P L A N T E N D E M IS M . L IM PO PO PR O V IN C E . SO U T H A FR IC A
IN T R O D U C T IO N
A new Plectranthus species apparently related to P.
xerophilus is described from the Sekhukhuneland Centre o f Plant Endemism (Van Wyk & Smith 2001) in the Limpopo Province.
Plectranthus porcatus was collected by the first author on the northern Leolo Mountain Range, while searching
P lectranthus porcatus Van Jaarsv. & P. J.D. Winter,
sp. nov., P xerophilo Codd similis sed corolla alba, caulibus
manifeste costatis, perspicue rectangularibus, cum basibus foliorum prominentibus persistentibusque differt.
TYPE.— Limpopo, 2429 (Zebediela): Sekhukhuneland, northern Leolo M ountain Range, Farm De Kamp 507
KS, 1 200 m, (-B D ), PJ.D. Winter 6725 (PRE, holo.).
Perennial, soboliferous, multistemmed, strongly aro matic shrub, ± 1.2 x 1.5 m; aerial stems sparsely branched.
Roots succulent, up to 14 mm diam. Stems herbaceous, semisucculent, woody at base, prominently 4-angled, lat erally com pressed decussately below nodes (distinctly rectangular, 1 0 x 8 mm in t/s), with a pair of longitudinal ridges from each leaf base, decurrent along angles on each side, usually continuing on two opposing sides through gap between next proximal leaf pair, to upper side of second leaf base; tomentose with translucent, m ulticellular hairs, often glandular-capitate, and sessile, orange, glandular trichom es; older stems somewhat terete, up to 30 mm diam., becoming scabrous due to fur ther growth o f verrucose trichome bases, rusty brown, longitudinally fissured in a reticulate pattern exposing
the green tissue below. Leaves recurved, conduplicate
unless mature and turgid, broadly ovate to ovate-deltoid, ( 5 5 - ) 9 0 - 12 0 ( - 2 10) x (4 0 -)5 5 -9 0 (-1 5 0 ) mm, older leaves progressively larger from growing tip; apex obtuse to acute, base shortly attenuate and decurrent on
petiole, margin serrate-dentate to serrate-crenate with 10-12 pairs of teeth 3-5 mm long, apical and marginal teeth with a cream-coloured spot visible on adaxial sur face, terminating veins that end in each tooth; thick-tex- tured, semisucculent, drying chartaceous, adaxial surface moderately glandular-pubescent, abaxial surface prom i nently reticulate-veined, densely glandular-tomentose, with sessile, orange-coloured, glandular trichomes, veins densely glandular-hairy and with similar sessile, glandu lar trichomes; petiole ascending, (7-)1 0 (-2 5 mm) long, conduplicate wings of decurrent lamina base often form ing a short channel, glandular-tomentose; abscission layer about 4 -6 mm from base, resulting in a distinctly raised leaf scar, adaxially obtusely v-channelled, abaxially rounded, comers shortly acuminate, with a decurrent ridge
on either side. Inflorescence a terminal racemoid thyrse,
200-400 mm long and with a pair of side branches at base carried on short peduncles up to 50 mm long; rachis square, 4 x 4 mm, reddish brown glandular-tomentose; bracts trian gular-ovate, acuminate, 5 x 4 mm, persistent or caducous.
Flowers in 7-flowered cymes forming 14-flowered verticil- lasters, the latter 20-30 mm apart; pedicels 8-10 mm long, densely glandular-hairy, apex inclined where attached to
calyx. Calyx 5.4-8.3 mm long (in fruit), densely glandular-
171 upper lip ascending, broadly ovate or broadly elliptic,
3.2-A.O x 2.7-3.0 mm, obtuse to acute; lower lip 4-toothed, teeth deltoid, 3 x 0.8-1.0 mm wide, acuminate; lower pair
of teeth slightly narrower and longer. Corolla 2-lipped,
somewhat sigmoid, 16 mm long, white to slightly mauve tinged, glandular-hairy and sparsely dotted with sessile, orange, glandular trichomes; tube 1.8 mm wide for 1 mm from base, then sharply inclined (diverging 45°-60° from raceme axis) for 4 mm, mid-tube ± abruptly bent down wards (vertically) for 5.5-6.0 mm, expanding towards mouth; upper lip spreading, unequally 4-lobed, two median lobes larger and 2 mm high (each with a group of sessile, orange-glandular trichomes on their adaxial side), lateral lobes obscure (0.5 mm long) and decurrent on mouth; lower lip boat-shaped, tilted down ± 20°, 10-12 mm long.
Stamens 4, didynamous; filaments adnate to anterior side of tube beyond bend, projecting from throat as a connate sta- minal furrow for ± 3 mm, free for ± 5 mm, mauve, curved out- and upward, exserted ± a third of length of lower lip; anthers versatile, 0.8 mm long, purple, becoming black;
pollen yellow. Style enveloped by staminal furrow, free for
± 5 mm; stigma bifid. Nutlets 1 mm long, smooth, dark
brown. Flowering time: late summer (January-March).
Conservation status: Data deficient (DD). Figure 10.
Diagnostic characters: Plectranthus porcatus is dis
tinguished from all other southern African Plectranthus
species by its peculiarly ribbed stems. The origin of these
ridges is not clear, but they appear to be associated with the petiole base. A possible explanation is that they are protruding bundle sheaths associated with deeper-lying leaf traces. Its raised leaf scars are quite distinctive.
Etymology: the epithet porcatus alludes to the ridged nature o f most stem intemodes. These ridges are absent on some intem odes during stages o f active growth.
Distribution and habitat: this species is known only from the type locality on the Leolo Mountain Range in Limpopo Province, South Africa (Figure 11), and we expect it to be found elsewhere only on the same part of this range, and doubtfully on dolomite of the Transvaal Supergroup on mountains to the north and east. The vege tation of the northern Leolo Mountain Range consists of dry Lydenburgia cassinoides-Kirkia wilmsii savanna. Rainfall is 400-600 mm per annum and occurs mainly from summer to autumn. The climate is subtropical, with hot summers and dry, sunny winters with light frost and
cool evenings. The populations o f P. porcatus were
encountered in very dark brown loam derived from gab- bro-norite rocks of the main zone of the Rustenburg lay ered suite in the Bushveld Igneous Complex (Viljoen &
Reimold 1999). P venteri Van Jaarsv. & Hankey, another
species endemic to the Limpopo River catchment in south
ern Africa (Edwards et al. 2000), occurs in the same area.
T A B L E 1.— M ain floral differences b etw een Plectranthus xerophilus and P. porcatus
P. xerophilus P. porcatus
C a ly x lo b es (relative size and shape)
C orolla
subequal unequal
colour m au v e/v io let w hite
length (m m ) ± 10 ± 16
m id-tube curvature (an gle o f d ivergence from m id to distal part o f tube, m easured along m id lin e o f tube)
± 6 0 ° ± 105°
orientation o f throat and mouth
outward ± dow nw ard
low er lip length (m m ) (4 - )7 1 0 -1 2
Stam en exsertion (proportional to length o f lo w er lip)
> 0 . 5 < 0 . 5
A FFIN ITIE S A N D PO ST U L A T ES FOR F U T U R E R E SE A R C H
The upper calyx lobe significantly larger than the lower
four is analogous to that of Plectranthus section Coleoides
(subgenus Plectranthus), as are the large hairy leaves. The
resemblance is superficial however, as the corolla tube is straighter in that section, and filaments are free.
Plectranthus porcatus shows a close, yet apparently
isolated, geographical relationship to P. xerophilus, in
semi-arid bushland of the Limpopo catchment (Figure 11). This situation suggests a close relationship between the two species, which are, in addition, both strongly aro
matic. P. xerophilus can easily be distinguished by its
subequal calyx, mauve corolla, and its unribbed, som e what terete, grey-tomentose stems. The main floral dif ferences between these two species are listed in Table 1.
P. xerophilus has till now been the sole representative of Plectranthus subgenus Xerophilus Codd. which was defined by the com bination of subequal calyx lobes, a hooded upper lip, and filaments shortly connate at the base. Any formal allocation of the new species to this group will, however, render the subgenus undefined, as the only remaining shared trait, namely shortly connate filaments, is by no means unique in the genus. The sig
moid shape of the corolla, similar to that of P. xerophilus,
is occasionally present in other groups as well.
TA BL E 2.— Points o f d ifference betw een Plectranthus porcatus and C odd's (1 9 7 5 ) subgenera
Su bgenus Salient character state in P. porcatus
Nodiflorus C odd ca ly x not subequally toothed: flow ers not sin g le nor in pairs in short pseu do racem es
Xerophilus C odd ca ly x not subequally toothed; corolla not galeate
Bumatastrum (B riq.) C odd ca ly x not subequally toothed Coleus (Lour.) C odd no differen ce in term s o f d iagn ostic
features
Calceolanthus C odd ca ly x throat not villou s Plectranthus stam ens not free at the base
Plectranthus xerophilus is not known from the Leolo Mountains (geologically part of the Bushveld Igneous Complex), but occurs on neighbouring substrates peripher al to the Igneous Complex, as close as within 20 km from
where P. porcatus was collected. As there seems to be no
topographical reason why the two species should not occu py the same area, we suspect this may be due to edaphic
specialization, as indicated by Siebert et al. (2001) for other
species in the Sekhukhuneland area.
From the differences listed in Table 2, it seems that
Plectranthus porcatus could well belong in subgenus
Coleus, currently comprising P. amhoinicus (Lour.) Spreng. and P. unguentarius Codd. Codd (1975) noted the existence
of exceptions referable to subgenus Calceolanthus in tropi
cal Africa, and thus unfortunately appears to have applied his subgeneric concepts only to southern African species, rendering his classification of very limited use in other areas. It is not clear why he did not refer these tropical
species to subgenus Coleus. If these atypical species are
included, there is no reason why P. porcatus could not
belong here as well. It further bears some resemblance to P.
barbatus Andrews (subgenus Calceolanthus) in. among other characters, the soboliferous habit and sigmoid corolla, and warrants further comparative study with some members
of that group. The relationships among subgenera Coleus,
Calceolanthus and Xerophilus therefore need to be revised
before P. porcatus can be confidently assigned to any one of
them. According to a recent plastid DNA phylogenetic
study (Paton et al. 2004), P. xerophilus is grouped in a much
larger ‘Coleus’ clade.
The conservation value of this species is considered relatively high, as it appears to represent a unique lineage
in southern African Plectranthus, whether or not it is
closest to P. xerophilus. It is currently threatened by cli
mate change, and while nothing is known about its uses or current exploitation, it may be predicted that its rarity, remoteness and strong smell are traits that could make it prized as a medicinal plant in future. Currently there does not appear to be any threat of harvesting in the part of the Leolo Mountains where it is known from, as it is too remote from the nearest settlement.
Further research into the infrageneric relationships
within Plectranthus could verify its conservation value,
and inform the authorities about appropriate conserva tion management measures.
The key in Codd’s (1985) treatment can be modified by inserting the following couplet to accommodate the new species, and renumbering subsequent couplets 13 to 55:
12a Leaf scar distinctly raised (4 - 6 mm); stem intem odes often with a pair o f additional longitudinal r id g e s...P. porcatus 12b Leaf scar not distinctly raised; stem intemodes never with a pair
o f additional longitudinal ridges:
ACKNOWLEDGEMENTS
Bothalia 35,2 (2005)
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