Taxonomy of the genus Pelargonium ( Geraniaceae ) : the section Polyactium ' 3 . The subsection

The subsection Polyactium of the genus PelargonitJm (section Polyactium) is treated taxonomically In view of currently available information. All species are geophytes with massive, naked underground tubers. Seven species are recognized, which have almost identical Rowers but differ greatly in respect of the morphology, texture, and indumentum of the leaves. All share a basic chromosome number of x = 11 : but polyploidy of up to hexaploid level occurs, with each species tending to have a characteristic level of ploidy. Six of the species are restricted to the winter rainfall area , while the seventh occurs in the winter rainfall area but also extends quite far into the summer rainfall region.


Introduction
The s ubsection Polyoetillm of Pelal'goniul11 section Polyactiul11 consists of 7 species. Like the subsections i\1agnislipulacea and Schi=opetala (Maggs, Vorster & Van der Walt 1995a), it has a well-deve loped underground tuber, but it is unique in hav ing pale mustard-yellow petals, with or without variably-developed very dark purp le (almost black) markings which may be expressed to sllch an extent that th e ye ll ow pigmentation is restricted to the margins of the petals. The flowers are almost regular, and dusk-scented. The subsection Cau/escenlia ( Maggs , Vorste r & Van der Walt 1995b) a lso has pa le m ustard·yellow petals, but usually without any black markings, an d lacking the underground tuber. Mos t ofthe species of subsection Polyactillm occur in the w inter rainfall reg ion, with only P. pulverulel1ll1m pene trating into the summer rainfall region along the east coast.
Ovary pear-shaped, 3.0 x 1.0- 1.5  to 130 x 140 mm; by the leaf segments being wider (up to 3 mm compared to 0.5-1.0 mm); by at least the basal segments branching off the rachis at a right angle instead of an acute angle; and by having 5 instead of 6 fertile stamens .

Flowering
Flowering specimens have been collected from September to the fo ll ow ing March, but most plants seem to flower during the summer months, from December to February (Figure 2). More than most other species in this subsection it tends to be evergreen .

Geographical distribution and habitat preference
This species has a fai rly restricted distribution range in the Western Cape Province, extending from Clanwilliam southwards to the Cape Peninsula ( Figure 3). This is a winter rai nfall area, w ith hot and dry summ ers; the annual rai nfa ll over most of this area being 300 to 400 mm. Plants of this species have been recorded at a ltitudes varying · 23 24 25 ,.  Bot. 1999, 65(2) -.-~, ,"-, --~_~J . ... .(";:t,\.,. , Pelargonium muftiradiatum: exposed parts, almost life-size. Based on van der Walt S. n Afr. J. Bot. 199t),65(2) from 150 to 1500111, mostly on sandstone-derived soils but occasionall y also on shale. It is a component of low, open fynbos.

History
i J • 1111fltiradiafUI1I was in cultivation in Europe in the early 1800 's and the original description is based on thi s cu ltivated material. Described as long ago as 1809, this species was lost for many years, so that its status as a natural species was questioned by Knuth (1912). It was only rediscovered in the 1930's when it was collected on the Cape Peninsula, on the lower slopes of Karbonkclberg (Salter 1938b). Since then a fair number of collections were made. but none again on the Cape Peninsula. This must rank as a species which has been severely depleted in numbers by agricultural and urban development.

Synonymy
A number of names were contemplated as possible synonyms of i). muiliradialll/11. but we came to the conclusion that they apply to hybrid plants, probably of garden origin: IJelargonilllJl sangllineunl Wend land : regarded as a hybrid between P. mu/tiradialum and P.fu/gidum (Linnaeus) L'Heritier by Knuth (1912), with which we concur. f> mros(lllgllineum Dietrich: listed as a synonym of P. sangui-Ileum by Knuth ( 191 2). No specimens could be traced, but from the desc ript ion it seems to be a hybrid.

Figure 6
Pelargonium anethifolium : exposed parts ¥1. lami na into very narrow linear segment s; but it is readi ly dist inguished by the lamina being less than 2x instead of at leas t 2x as long as wide, by the indumentunl of the lamina being inconspicuous to the naked eye instead of mostl y dense ly hirsute (at least in narrow-segmented forms), and havi ng 6 instead of 7 fertile stamens. In P. mu/liradialUm Wendland (p. 11 7) the lamina is also di vided into li near segme nts; but in th at speci es the segments arc conspicuously wider (up to 3 rnm wide), and the pl ant is altogether much larger with lamina up to 45 0 x 450 mm and up to 15 or even 30 flowers pe r pseudo-umbel. In addi tion, at least the lowermost regments branch off the rachi s at close to a righ t angle , whereas in P. anethi/o/ium they branch off at an acute angle. (n P mu/tiradiatum we observed on ly 5 fertile stamens per fl ower, in contrast to 6 in P. anethifolillm.

Flowering
Plants fl ower fro m October to December, with a peak in October and Novem ber, after which the exposed parts die back for th e remainder of the summer (Figu re 7). Thi s period is much shorter than in P IriSle, which flowers almost throughout the year.

Geographical distribution and habitat preference
This species is confined to the western part of the Western Cape Provin ce, from Vanrhynsdorp so uthward s to the Cape Peninsu la (F igure 8). A record from the Bushman's River Mouth (Zeyher /76) is doubted and asc ribed to incorrect labelling. It is not a very common species, which may be attributed to urban and

121
intense agr icural development throughout its distribution area. It occurs on the sandy coastal flats as well as on stony soil in the adjacent mountain ranges on substrates derived from sandstone, at a lti tudes of 100 to '1600 rn . A long the coast it occurs in Sandve ld vegetation, and in the mountai ns it is a component of Arid Fynbos. The annual ra infall over its distribution area varies fro m 200 m m near the coast to about 600 mm in the mountains, occurring predominantly during the winter months. During the hot and dry summers P. ane/hi/olium is dormant and deciduous after flowering.

History
Fi rst desc ri bed in 1835 by Ecklon a nd Zeyher from material collected by themselves, this species has subsequently only scantily been collected. T he expl anation for this must be that it has largely been eradicated by habitat destruction due to widespread wheat cu ltivation through out its former di stributi on area, and urban developm ent at the south ern end of its ran ge.

Synonymy
Pe/argonilll1l callosum was published as a nomen nudum by E. Meyer in 1843 . Harv ey (1860: 273) noted that its leaves were even more glabro us th an normal for P. anethifo/ium , but concluded that it is neverthe less conspeci fi c with P. anethi/olimn. We examined the material cited by Meyer (Drege J 28() in G, L, P, W) , and concur with Harvey ' s (I.e.) conclusion. Previous illustration: Salter: t, 6 ( 1938a) .
Ovary ovoid, ca. 3.5 x 1.5    Diagnostic features P. pi/lansii resembles P. pu/verll/entunJ Sweet (p. 123) by its glaucous leaves with the lamina decurrent along the petiole; but differs in that the lamina may be pinnatifid or even pinnate and never laciniate nor ciliate, and by the markings on the petals being inconspicuous or absent compared to the very prominent purple-black markings in P. pulverulentum. In P. pillansii the chromosome number is mostly 20 = 22, while in P. pulverulenfum it is 20 = 44. P. pil/ansii is a Western Cape species; and its replacement by the morpholog ically not dissimilar P. pulvel'/(-lentul11 in the Eastern Cape and KwaZulu-Natal may be indicative ofa closer than specific relationship between the two taxa.

Flowering
Plants flower from February to April, i.e. in late summer and autumn , usua ll y before the commencement of th e ra iny season (F igure 11 ), and are leafless at the time of flowering.

Geographical distribution and habitat preference
This species has a wide distribution in the winter rainfall region of the Western Cape Province, from the Gifberg southwards to the Cape Peninsula, and thence eastwards to the Langkloof/ Mountains (Figure] 2). It occurs in fynbos vegetation, on sandsto ne or shale, and is often found within rock fissures. The rainfall is in the region of 200 to 400 mm per annum , but accurate figures are not available because the plants prefer mountai nous areas from where rainfall data are absent. The species is rare on the Cape Peninsula, having last been collected there in 1946, and the reason for thi s may be that the rainfall is too high for it. Pillans, who recognized it as a new spec ies. Description was delayed by its unusual rarity, on ly being effected in 193 8. Si nce then it was found to have a considerably wider distribution, and its rarity in the vicinity of the Cape Peninsula probably dignifies that that area is at the periphery of its distribution area.  Bol. 1999, 65(2) .i! / J.  s. Air. J. Bol. 1999. 65(2) 1. 146 ( 1924); Leighton ( 1932); Batten & Bokelrnann: 1. 73.1 (1966); Van der Walt: opp. p. 37 (1977) A geophyte with exposed parts poorly developed, deciduolls, unarmed. up to 600 mm tall \vhen in flO\vt:r. b:posed stems smooth, hard and woody, densely str i gos~ and hirsute with scattered glandular hairs, initially green but turning brown with age, up to 500 mrn long and 5-10 mm th ick. Leaves basal, simple to (3-)5(-7)-pinnatitid to pinnatisect or occasionally 3-fol iolate, lamina decurrent along petiole, coriaceous, conspicuously ciliate, glabrous but occasionally dt:nsdy pubescent, glaucous; lamina ovate to cordiform in outline, hasi! cordate, apices of segments rounded to almost acute, 35-1 20 x 3()-130 mm ; petiole up to 200 mm long, deciduou s; stipules cordiform to ovate with apices acute, 4-10 x 3-8 mm, membranous hecom in g scarious, conspicuous ly ciliate, abaxially densely strigose hecoming glabrous, with sparse glandular hai rs. Inflorescence a stout unbram:hed peduncle 100-150(-400) mm long and up to 3 mm in diameter. carrying a pseudo-umbel of 5-10(-18) al most regular flowers. Pedicel much shorter than hypanthium: 2-20 mm long, densely strigose and with glandular hairs. Hypanthium 20-50 mm long. Sepals narrowly ovatc with apices acute, practically glabrous hut hirsute at apices and villous along adaxial margins, yell ow·green to brO\\'n tinted with red , margins hyaline, 7-10 x 1-2 mm. Petals 5. dull yellow. spathulatc; posterior two 1O~1 4 x 3-6 mm, rcflexed at ca. 90° ncar base and slightly inflexed at apex. without markings or .st reaked wi th pu rple-black; anterior three slightly narrowe r: up to 5 111m wide. orientated similarl y to posterior petals hut less markedly rdlexed, \vith entire cent ral area uniformly purple·black leaving only a narrow dull yellow margin. Fertile stamens 6 (4 long, 2 short and equalling staminodes), pol len bright yellow. Ovary pear-shaped, .J -5 x 2 111111, densely covered in apically-directed hairs, pale green; style ca. 2 mm long; stigma 5·branched, deep maroon ; mcricarp base 8-9 mm long, lai135-45 mm long. (Figure 14 AfT. J. Bot. 1999, 65(2)

Diagnostic features
Due to the remarkable variabi lity of its foliage, P. pulverulentum is often confu sed with other species in the subsection. The densely pubescent form can be confused with the consistently ve luti nous P. lobatum, but in that species the base of the lamina is never decurrent. The more com mon glabrous form ean be confused with P. pillansff, but is easily distinguished by the ciliate leaf margins; furthermore P. pulvemlentum is an Eastern Cape and KwaZulu-Natal species w hile P. pillans;{ is known from the Western Cape only.

Flowering
Plants flower from Jul y to the following April , but predo minant ly from September to March (Figure 15). Il is deciduous during the winter months.

Geographical distribution and habitat preference
This species is known from Mtunzini in northern K waZulu-Natal, southwards to Hwnansdorp (Figure 16), at altitudes varying from sea level to more than 1600 m. It is a component of grassland , often on sandy so il s. Th is area rece ives a summ er rainfall amou nting to 600-1 000 mm per annu m, and it is unexpected that a species occurring under such relative ly wet conditions compared to the other species in the section, should have such glaucous and leathery leaves.

Synonymy
Pelargonillnl pedicel/alum Sweet, treated as a variety of P JlII/"'I'/II<lIIlIIn by Harvey (1860) and Knuth ( 191 2), was distinguished on account of its longer pedicels and bracts. The present study reveal ed these structures to vary widely and continuously, so that separate taxonomic status cannot be justified.
PelargoniunJ pulverulentum var. fanafoserieeum Knuth was di stinguished on accou nt of its dense foli ar indumentum. Hairi· ness of the leaf was, however, found to be another cont inuous ly variable characteristic so that the variety cannot be upheld.
unanm:J , up to 500 mm tall when in flower. E'posftd sIems smooth, hasally hard and woody , di stally herbaceou s and densdy vc lutinou s and with numerous glandular hairs. initially green but turning brown \vilh age. up 10 900 mm long and 5-8 mm thick

Flowering
The floweri ng period is well defi ned , stretching from June to December with a marked peak in September ( Figure 19). annual rainfall varies between 400 and 600 mm, but at the extreme north-western end of the range it may be less than 200 111m . It is commonly associated with fynbos, along the sandy coas tal flats and some 150 km inland on the foothills of the mountain ranges.
membranous becom ing scario lls, sparse ly ciliate, abaxially densely strigulose becoming glabrous, with scattered glandular hairs. Inflorescence a stout unbranched peduncle up to 200 mm long and up to 3 mm in diameter, carry ing a pseudo-umbel of 4-20 almost regular flowers. Pedicel much shorter than hypant hium : 1.0-2.5 mm long, densely stri gose and with glandular hairs. Hypanthillm 20--55 mm long. Sepals narrowly ovate with apices acute, abaxiall y densely strigu lose and with scattered glandula r hairs, ad axially glabrous, margins ci liate, yellow-green with apices red and margins hya line, 6-10 x 1-3 mm. Petals 5, alm ost equal , 11 -18 mm long, dull ye UO\v to flesh-coloured with maroon to purple-black. mark.ings. spathulatc with apices rounded; posterior two 4.0-5.5 mm wide, reflexed at co 90° near base and slightly inflexed at a pex ; anterior three 3.5-5.0 mm wide, orientated s imilarly to posterior petals but less markedly reflexed . Fertile stamens 7 (4 long, I medium , 2 short and equalling staminodes), pollen golden yellow. OVQfY pear-shaped, ca. 3 Diagnostic features P. radulifolium is distinguished by its erect, pinnate to 2-pinnatifid leaves of which the lamina is 2 to 3 times as lo ng as wide, membranous, not glaucous, and adaxially often densely strigose to hirsute. In P. pillansii (p. 121) the lamina is also pinnate to pinnatifid; but almost as long as w ide. leathery. glaucous, and glabrate .

Flowering
It is a sum mer-flowering spec ies, with its fl owe ring period extending from August to Apri l with a peak in January and February (F igure 23). Synonymy For many years this species was erroneously known as P. hel'Gd eifvlium Loddiges [e.g. Knuth : 354 (1912)], but examination of the type showed that that name should rather be in the synonymy  Geranium pasNnaci/olium Miller, T he gardener's dicti onary ed. 8: 37 (1768), ex descr. Type: not designated.
A geophyte with exposed parts poorly developed, deciduous, unarmed, usually about 250 mm but occasionally up to 500 mm ta ll wh en in fl ower. Exposed stems rough due to stipul ar and petioiar scars, basally hard and woody, dista lly succu lent, in itially green but turning brown with age, up to ISO mm long and 5-10 mm thick. Leaves basal, erect to prostrate, pinnately to 4-pinnatifidly divided int o lin ear segments usually about 1 m m w ide but occasionally up to 8 mm wide in leaves wi th poorly differentiated segmentation, herba· ceous, usually covered in a dense. short. hoary indumentum wi th short gland ul ar hairs interspersed; lamina at least 2 times as long as wide, bases of segments attenuate and often petio/ulate, apices of segments rounded or truncate, margin s entire and involute, 100-450 x 40-150 mm ; petiole up to 120 mm long, deciduous; stipules cordiform to ovate with apices acute, 5-8 x 6-1 0 mm, membranous becoming scarious. abaxially initially dense ly pubescent. Inflorescence a stout unbranched peduncl e 50-250 mm long and up to 2.5 mm in diameter, carrying a pseudo-umbel of 6-15 almost regular fl owers. Pedicel much shorter than hypanthium: up to 4 mm long, densely strigose and with glandular hairs. Hypanlhium 30-55 mm long. Sepals narrowly ovate with apices acute, abaxially densely strigose and with sparse gland ular hai rs, adaxially glabrous, margins ciliate, yellow-green to dull green and occasionally russet-ti nted with margins hyal ine, 5-7 x 1-3 mm . Petals 5, almost equal, 10-18 mm long, uniformly pale yell ow or wi th wine-red or purpl ish black mark ings leaving only a border of ye llow, spathul atc with apices rounded; posterior two 4-8 mm wide, reflexed at ca. 90° near base and Slightly inflexed at apex; anterior three 2.5-6.0 mm wide, orientated si milarly to posterior petals but less markedly reflexed. Fertile stamens 7 (4 long, 3 short and equalling staminodes), pollen bright yellow. Ovary pear-shaped, 3.5-4.5 x 2.0 mm, dense ly covered in apically-directed hairs, pale green; style 2.0-2.5 mm long; stigma 5branched, reddish; mericarp base 7-10 mm long, tail 35-45 mm long. (Figures 27 and 28

Diagnostic features
P. Irisle is distinguished by its lamina being at least twice as long as wide, usually conspicuously pubescent, divided into linear segments which are usually about 1 mm wide but may be up to 8 mm wide in leaves in which segmentation is poorly developed, and 7 fertile stamens per flower.
In the only other species in this subsection in which the lamina is divided into linear segments, P. anethifolium and P. muiliradiatum, the lamina is almost as wide as long and at least adaxially the indumentum is inconspicuous. Furthermore, P. anethifolium has only 6 fertile stamens, and P. multiradiatum only 5.

Flowering
In this species flowers have been recorded practically throughout the year, but there is a marked peak from September to December ( Figure 29).
Geographical distribution and habitat preference P. triste occurs commonly throughout the Northern and Westem Cape Provinces, from the Orange River southwards to the Cape Peninsula, and then eastwards to near Mossel Bay (Figure 30). It is very common on the coastal sandy flats, but also occurs in more mountainous terrain at altitudes of up to 1800 m. This distribution falls entirely within the winter rainfall region, but as can be expected from such a wide distribution and altitudinal range, there is a considerable range in the annual rainfall, from about 100 mm to at least 600 mm. It is conspicuous in open places ( Figure 28), but as succession progresses and the plants get overgrown by surrounding vegetation they stop flowering and become progressively more inconspicuous. Nevertheless, the substantial underground tuber enables it to survive for many years in semi-aestivation, as S. Arr. .I. Bot. 1999. 65(2) manifested by the sudden profus ion of flowering individuals after a fire.

History
This was arguably the first species in the subsection to become known to the scientific world, being common around Table Bay where the earliest explorers casted anchor. The oldest known literature reference is in Coruui's Canadensium plan/arum of 1635, which includes an illustration (our figure 31). Codd and Gunn (1982) related how the material on which this reference is based was probably collected by the French explorer De Beaulieu at Table Bay on the 24th May 1622.
In the first edition of Linnaeus' Species plan/arum the concept of Geranium Irisle was broad and included what is now known as Pefargonium laba/um. As soon as 1759 Burman f. emended Linnaeus' concept by accepting Geranium lobalum as specifically distinct.

Synonymy
Being a common species, P. trisle is well represented in herbaria. The long list of synonyms reflect its variability in respect of the degree of foliar division and flower size.

Discussion
The aim of taxonomy is not only to define taxa, but also to classify them according to their perceived evolutionary context. Our views on the position of this group within the section Pofyactium  have been stated previously (Maggs, Vorster, & Van der Walt;1995a), and, therefore, our present concern is the relative taxonomical position of the species within the subsection Po/yactium.
The present geographical distribution of the subsection falls almost entirely within the winter rainfall area, with only one species (P. pulverulentum) extending significantly into the summer rainfall region. This suggests an origin in the winter rainfall region. At present the highest concentration of species (Le. centre of diversity) is along the south-western coast, between Cape Town and Lamberts Bay, where five species have been recorded in each of four adjacent one degree squares, with some growing in close proximity to each other ( Figure 32). Further northwards along the west coast the concentration of species rapidly diminishes un til the north-western arm of the subsection's crescentshaped distribution area is represented over a distance of about 300 km by a single species, P . ll'iste. North-eastwards of Port Elizabeth only a single species occurs (P. pulverulentum), extending far into the summer rainfall region and covering an area almost as extensive as the remaining species in the subsection together.
Expressed in terms of the number of one degree squares in which each species has been recorded, P. plllvel'ulentum has the widest distribution (18 squares), closely followed by P. triste (16 squares) and P. /obalum (15 squares). The species with the smallest distribution range is P. multiradiatum which occurs in only 3 squares.
With a basic chromosome number ofx = 11, polyploidy up to the level of hexaploidy has been noted. rt is tempting to deduce that the level of ploidy tends to increase proportipnally to the distance from the centre of diversity (Figure 33), thus supporting the hypothesis that adaptive radiation took place from an archtype with 2n ~ 22 along the south-western coast, to higher ploidy levels further away from the presumed area of origin. However, close examination of the data shows such a conclusion to be unwarranted. The higher ploidy levels along the east coast, furthest away from the centre of diversity, are representative of a single species (P. pulverulentum) which in general tends to have high levels of ploidy. High ploidy levels, up to 2n ~ 66, occur throughout the geographical range of the subsection, including the centre of diversity.
Our data suggest that there is a tendency towards set ploidy levels within some species. Thus P. lobatwn, P. multiradiatum, Figure 32 Pelargonium subsection Polyactium : known geographical distribution and concentration of species, on a resolution of one degree square (approximately lO 000 m 2 ). S. Atr. J. Bot. 1999,65(3)  and P. pillansii both have 2n = 22, P. anethifolilltn has 2n = 22 or 44, P. triste has 2n = 44 or 66, and P. radlfl~folillm has 2n =; 66. It is noteworthy that four of the seven species show a range of ploidy levels, the most remarkable being P. pulverulentum with 2n = 22, 44, and 66. In general, those species with the widest geographical distribution also have higher levels of ploidy as well as a wider range of ploidy levels. Thus P. mllltil'adiatllm. occurring in only three one-degree squares, have 2n = 22; while P. Iriste (16 one-degree squares) have 2n ~ 44 and 66, and P. pulverulentum (18 one-degree squares) have 20 = 22, 44, and 66. We speculate that a range of ploidy levels, ifnot higher levels of ploidy, enables a species to utilise a wider range of ecological niches and so occupy a wider geographical area.
There does not seem to be any relationship between level of ploidy and morphology. Thus chromosome numbers of 2n ;= 22 were observed in P. lobatum and 2n = 22, 44, and 66 in P. pulverulentum, the two species with the least divided leaves which we consider to be an ancestral or more primitive trait. Parallel with this we observed 2n = 22 in P. tnultil'adiatultl and 211 = 44 and 66 in P. triste, both species with extremely divided leaves which we consider to be a derived (relatively advanced) trait.
Like in two of the other three subsections of section Polyac-{jum, the flowers of the individual species within the subsection Polyactium are practically identical. Not on ly can the flowers not be used for taxonomical purposes, but they also seem unlikely to constitute effective barriers against interspecific hybridization (the flowering times of the individual species vary, but there is considerable overlap). The interspecific variation is instead manifested by leaf morphology, expressed by degree of inc ission, texture, indumentum, length/width ratio, and spatial orientation. Barriers against interspecific gene-flow are probably located in individual responses to environm ental conditions, resulting in subtly different habitat preferences leading to spatial separation.
The distribution of these species coincides largely with that of the winter-rainfall fynbos vegetation, but P. plllverulentultl is largely a component of summer-rainfall short grassland. Within these major vegetation types, the species occur under conditions of considerable seasonal climatic fluctuations. Summers tend to be hot and dry, and winters cool and wet over most of the range; whereas in the summer-rainfall grassland, winters tend to be drier than the summers but sunnier and probably warmer than in the winter-rainfall fynbos.
severe. It was probably in response to these restrictions that the well-developed underground storage organs evolved, in order to survive the inhospitable season.
Typical climatic features of the subsection's distribution area are rainfall above 200 mOl per year, hot summers, and cool winters wi th out frost. In the west the climate is of the Mediterranean type with dry summers and wet winters, further eastwards the ra in fa ll becomes increasingly non-seasonal, culminating in a summer-rainfall region along the east coast north-eastwards of Port Elizabeth. Quantitatively the rainfall is influenced by local topography and largely depends on the exposure of the site to coastal winds. Coastal localities seldom get more than 750 mm com pared to nearby mountain slopes which may receive twice th is amount, whereas inland valleys get on ly 200 to 400 mm (F uggle & Ashton 1979). In the winter-rainfall area of the Western Cape, rainfall occurs almost exclusively as prolonged and gentle drizzles; whereas in th e eastern, summer-rainfall regions precipation often takes place as violent thunder storms during the summer months.
The proximity of oceans to the distribution area of the subsecti on has a moderating influence on temperature, and frost occurs rarely. The coastal belt is also characterised by frequent stron g winds, and th e low or even prostrate growth form may be a reacti on to this factor. The subsection Po/yacliutn is largely confined to sandstonederived soi ls, which are poor in nutrients and very well drained. Neverthe less, some individuals, especially of P. lobatum, also occur on soils derived from shales, which are clayey and comparatively richer in nutrients.