THE WEEDY FERNS OF FERNCL]

Unusual invaders threaten Natal’s flora

by Neil Crouch, Pi e term ari tzburg

Above. Adiantum raddianum, delicate but alien.

ention alien invaders, Right. Lunathyrium and Hakea, Australian japonicum, acacias and bugweed, perhaps our most M aggressive fern ) along with a horde of other aggres­ . invader. Since its 2 sive weeds, normally come to 1 introduction in the 0 mind. Ferns, on the other hand, early 1980s, this 2 weed has spread d conjure up an image of tranquil e widely through the t scenes in unspoiled virgin forest, a forests of Natal. d Photos: N. Crouch. ( complete with kloofs, moss and r

e earthy scents. Yet today, all is not h s well in the depths of the forest discover that the diversity of ferns species. The strikingly attractive i l tree maidenhair fern, Didymoch- b shade. here is greater than that of the u At Ferncliffe Nature Reserve in entire British Isles. Ferncliffe is laena truncatula, shelters in the P

e Pietermaritzburg, exotic ferns have situated along an escarpment stream-side shade, surrounded by h t

invaded the forests - 6 species now within the Natal mistbelt a host of spleenworts. Fifteen such y

b Ngongoni veld (at an altitude of species occur here and include

live amongst 60 or so of their d 1 000 m) and lies on Table Asplenium preussii, A. protensum, e indigenous relatives. In common t n with all weeds, these naturalized Mountain Sandstone. Many inter­ A boltonii and A. gemmiferum. a r ferns show aggressive, invasive esting and diverse plant forms Covering the surrounding boulders g

e characteristics and consequently thrive in these conditions, the very rare ‘wavy filmy fern’, c n disturb the natural status quo. It including Begonia geranioides, Trichomanes reptans, hides e c i appears that these aliens are Streptocarpus fanniniae, and amongst its more common relative l

r quietly securing a foothold and Clivia miniata. A high annual rain­ the black-haired filmy-fern, e d insidiously spreading, not only fall, much of which is in the form T. melanotrichum, and the fragile n u within Ferncliffe, but across the of mist, ensures a luxuriance of bladderwort, Cystopteris fragilis. y Natal midlands. Perhaps not all life in this forest patch. However, a w 6 ferns have the potential to the climate has also proved suit­ Adiantum raddianum e t able for pine and wattle planta­ Known popularly as the delta a severely impact on the indigenous G

flora, but their presence and tions, stands of which today share maidenhair fern, this Adiantum t e ascendancy here cannot be noted the Ferncliffe Nature Reserve with species boasts nearly 70 different n i remnants of what must once have cultivars, several of which have b without some concern. a been a magnificent forest. escaped into moist situations as

S The Pietermaritzburg munici­

y pality today owns and controls the Despite this, the reserve is rich far afield as Ceylon and the Lesser b in ferns and fern allies, including Antilles. It has a natural distribu­ d reserve which is a mere 4 km long e c and Vz km wide. It is startling to several rather rare and unusual tion ranging throughout the tropi­ u d o r 88 Veld & Flora September 1994 p e R Left. Doodia caudata Doodia caudata, After probably escaping from the the small rasp fern - a likely escapee Natal Botanical Gardens in from the Natal Pietermaritzburg, this species has Botanical Gardens in Pietermaritz­ been actively on the move and burg. may now be encountered near Howick, at the Umgeni Valley Below. The golden fern, Project. Doodia is closely related Pityrogramma to our indigenous blechnums, but calomelanos, colo­ it is a native to Australia and nizing a roadside bank. The common Tasmania where it is locally name is derived known as the small rasp fern. from the character­ Maoris call this fern ‘moki moki’ istic yellow, pow­ dery under-surface and use it in the preparation of of the fronds. perfumes. Photos: N. Crouch. In Ferncliffe, Doodia prefers moist roadside banks in the shady pine plantations and may usually be found growing in colonies alongside Blechnum australe. With its ability to survive in a wide range of habitats it is quite conceivable that Doodia will greatly expand its distribution range in the years to come.

Pityrogramma calomelanos var. aureoflava This highly decorative fern possesses a farina, or dusting of yellow powder on the underside

) of the frond. Not surprisingly, it is .

2 known as the ‘golden fern’ and is 1

0 popular as a horticultural 2

d potplant or bedding subject. e t Originally of South American ori­ a d gin, the golden fern has now natu­ (

r ralized in Ferncliffe and at several e h

s cal Americas, from the Caribbean, and the Karkloof Forest near sites in the Transkei, Natal and i l south to Argentina. In South eastern Transvaal, often well away b Pietermaritzburg. Of the 6 species u Africa this species has naturalized outlined in this article, from human settlements. Jacobsen P

e in a region extending from the Lunathyrium is by far the most described this plant as a ‘migrato­ h t

Cape to the eastern Transvaal. aggressive invader; its spore ry pioneer fern’ and true to charac­ y b Despite its graceful guise, this fern dispersal is highly effective and ter, Pityrogramma has colonized

d has multiplied phenomenally and colonies are quick to establish in .moist clay road cuttings in the e t

n today is probably the most abun­ new localities. As with Doodia, reserve. a r dant fern species in the forest. In the Japanese lady fern appears to g

e Ferncliffe, specimens representing tolerate the tannin-rich soils of Macrothelypteris torresiana c n several ‘cultivar escapes’ may be exotic plantations; a clear demon­ This handsome lacy fern is per­ e c seen. i stration of its adaptable weedy haps named after the Torres Straits l

r character. From the security of between Papua New Guinea and e d Lunathyrium japonicum these alien stands, advances by Australia, where it naturally n u Burrows (1990) notes that before this lady fern are made on the occurs. Although in South Africa

y 1978, Japanese lady fern, neighbouring indigenous forests.

a its exotic status was initially w Lunathyrium, was not found grow­ Ironically, this species was first debated, it is today generally e t ing wild anywhere in Africa. Yet a described as Asplenium by accepted that Macrothelypteris

G just 5 years later specimens were Thunberg, after his eighteenth cen­ is introduced. Macrothelypteris t e discovered growing at Mapumulo tury sojourn in the Cape of Good torresiana is believed to have orig­ n i near the lower Tugela, probable Hope. He may have first collected b inally escaped from the Durban a escapees from the long-established it upon his arrival in Japan, where

S Botanic Gardens where it has been

y mission station. Since then plants Lunathyrium is native, as it is to in cultivation for over a century. b have been collected as far afield as most of the Far East. d In the intervening years it has e c Swaziland, the Natal south coast spread mainly along the Natal u d o r Veld 6- Flora September 1994 89 p e R south coast and, to a lesser degree, inland. Elsewhere in the world this species has been similarly introduced, one new range extend­ ing from the U.S.A., southwards to the tropical Americas. In Ferncliffe, Macrothelypteris appears to be a recent arrival.

Nephrolepis exaltata In its native state in the Caribbean, the fronds of the ‘sword fern’ may extend for up to 2.5 m in length. Yet in Ferncliffe fronds of 50 cm are more usual, with pinnae which are contorted and frilled in a variety of horticulturally selected traits. Nephrolepis is actively spreading through the indigenous forest patches, most commonly along the path-sides. The parent stock for these plants was proba­ bly planted in the garden of the stone farmhouse, built in the 1850s by the resident stonemason, Jesse Smith. Today the farmhouse serves as an environmental educa­ tion centre. In addition to the above 6, a seventh fern weed may be found taking refuge in the Ferncliffe

) reserve. This is Adiantum hispidu- .

2 lum , the ‘rough maidenhair fern’, 1

0 which was previously known from 2

d the Town Bush region and today e t may still be found as an escapee a d behind the Natal Botanical (

r Gardens. In an ironical twist, sub­ e h

s urban developments on the i l

b reserve boundary may have result­ u ed in the local eradication of this P

e introduced species. h t

In recent years several indige­ y b nous fern species have been con­

d spicuously absent in the vicinity e t

n of Ferncliffe. despite extensive a r searches. Elaphoglossum aubertii, g

e Cyathea capensis and Lycopodium c n verticillatum are three examples of e c i ferns apparently now locally l

r extinct. One might surmise that e d their loss is most likely due to a n

u combination of factors: the effects

Further reading Top. A specimen of what is probably the y of forestry and urban expansion, Burrows, J.E. (1990). Southern African ferns most recent fern invader in the Ferncliffe a and fern allies. Frandsen, Sandton. Nature Reserve, Macrothelypteris torre- w theft of indigenous species and e Goudey, C.J. (1985). M aidenhair ferns in siana. t

a competition with weeds. Ferns as cultivation. Lothian, Sydney.

G Jacobsen, W.B.G. (1989). The ferns and fern Above. The sword fern, Nephrolepis weeds may be no exception. t allies of southern Africa. Butterworth, exaltata, growing at the base of a young e Although the influence of fern n Durban. Cyathea dregei. Photos: N. Crouch. i invaders on indigenous ferns has b Jones, D.L. & Clemesha, C.S. (1981). a not been well documented, it Australian ferns and fern allies. Reed S Press, Sydney. y seems that the 6 unusual invaders b Schelpe, E.A.C.L.E. & Anthony, N.C. (1986). mentioned in this article have also d Flora of southern Africa: Pteridophyia. e c had an impact. © B.R.I., Pretoria. u d o r 90 Veld & Flora September 1994 p e R