PlantLife Volume 51.5 July 2021 Actinanthella wyliei (Loranthaceae): a rare mistletoe endemic to Ngoye

 

In search of Actinanthella wyliei (Loranthaceae): a rare mistletoe endemic to Ngoye Forest

Sharon Louw

Ezemvelo KwaZulu-Natal Wildlife, P.O. Box 13053, Cascades, 3202, South Africa.

 

Background

The mistletoe Actinanthella wyliei (Sprague) Wiens, is a poorly known, restricted-range species endemic to Ngoye Forest (also known as Ongoye Forest Reserve), KwaZulu-Natal. This parasite has been recorded as growing on Erythroxylum, with an uncertain flowering period and with flower descriptions based on only a few herbarium specimens. According to the available literature, the fruit is unknown. The species’ conservation status is currently listed as Least Concern.

 

Figure 1: Actinanthella wyliei in flower

 

Figure 2: Location of Ngoye forest

Figures 3 a & b: A. wyliei habitats at Ngoye Forest

During a lull in coordinating Chacma Baboon counts at Ngoye Forest in 2013, I wandered along the edge of the forest and found and photographed the last flowers of a “mistletoe”. I wasn’t able to identify the plant from my books and it was only when I saw a photograph of A. menyharthii (a species known from Zambia, Zimbabwe and Mozambique) in a presentation that Prof. Braam van Wyk gave at a CREW workshop that I realised that I had photographed A. wyliei. In fact, according to Braam, mine were the first photographs of the fruits! Because so little was known about the plant, I decided to do some work on the species with the following objectives:

(1) investigate the abundance and distribution of A. wyliei within Ngoye Forest;  

(2) verify the flowering and fruiting period;

(3) describe the habitat of the species.

A search for individuals of Erythroxylum pictum (Forest Coca-tree), the possible preferred host tree of A. wyliei, was conducted in the eastern section of Ngoye Forest. While E. pictum occurs more widely in the reserve, it is commoner in the east, where the habitat is more suitable. I also have not seen A. wyliei in other parts of the forest yet, nor have I seen it growing on E. emarginatum (African Coca-tree). The study area comprised approximately 588 ha within Ongoye Forest Reserve and the neighbouring Mzimela Traditional Council Area. The co-ordinates of E. pictum trees with A. wyliei present were recorded using GPS technology. A. wyliei plants were monitored over a two-year flowering and fruiting cycle. Data recorded included bud, flower, fruit and leaf measurements. Field observations included morphological descriptions, photographic records and habitat descriptions.

 

Figures 4: A. wyliei flowers illustrating wide vents in mature buds.

 

Fig. 5 (a & b). Characteristic coiled anther filaments at anthesis.

A. wyliei is uncommon and was only recorded on mature individuals of E. pictum. I recorded the parasite on 48 trees and some trees, particularly the larger ones, were host to several parasites. Like the host tree, its distribution in the eastern section of Ngoye Forest (which extends into the Mzimela Traditional Council area) is limited to forest margins and scattered forest patches associated with granite outcrops. Typical plant community associates are listed in Appendix 1.

The peak flowering period for the species is March, and flower initiation begins in February and extends through to April, although some flowers can be found as late as September. Flowers are borne singly or in groups of up to three in leaf axils. An immature Grey Sunbird was observed visiting the flowers.

Fruiting commences in late May with most ripe fruit observed in June and July. Fruit development is staggered, with developing and mature fruits simultaneously present. The fruit is a bright red-orange berry. About half the fruits were parasitised. Removing the fleshy skin reveals a bright orange aril. Removal of the aril exposes a white seed, with a green pre-emergent haustorial attachment visible at the tip. The entire seed is covered with a clear sticky substance which readily attaches the seed to a branch.

Leaves are hairless and light green with no colour difference between the surfaces. Margins lack serrations, although in certain leaves they are wavy. Mature leaves develop a thin red line along the leaf margin. The midrib is obscure. Leaf blades break cleanly and no threads, latex or other exudates are present.

Average measurements for parts taken from 15–20 plants are recorded in Table 1.

Table 1. Flower, fruit, seed and leaf measurements (mm).

Flower bud	Flower	Fruit	Seed	Leaf
45.73	44.8	11.78	6	19.2

  

Fig. 6 (a & b). A. wyliei fruits topped by the circumscissile calyx.

Fig. 7 (a & b). Haustorial attachment emerged from seed.

Fig. 7. A. wyliei seedling on host E. pictum.

Conservation threats and further work

A. wyliei occurs in low densities in the eastern section of Ngoye Forest on a single host, this being mature E. pictum trees. While fire has been part of this landscape for a long time, hot and frequent wildfires present a threat to the host and its habitat within the rocky outcrops at Ngoye Forest. Any reduction in host numbers will have adverse effects for A. wyliei. Wildfires need to be controlled, particularly within Ongoye Forest Reserve. Given the species’ small range, the threats it faces and its habitat specificity, its conservation status should be reassessed.

Sufficient data are now available to complete the morphological description of this range-restricted species. Further investigation into the pollinators and dispersal agents of the species would be helpful.

Field observations were limited to the eastern section of Ngoye Forest and future searches for A. wyliei need to be expanded across the rest of Ngoye Forest to get a full understanding of the A. wyliei population.

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Appendix 1: Rocky outcrop forest community members of the eastern section of the Ngoye Forest.

Species typical of the rocky outcrop forest community
Acridocarpus natalitius var. natalitius	Erythroxylum pictum
Agapanthus sp.	Freesia laxa
Albizia adianthifolia var. adianthifolia	Haemanthus albiflos
Aloe rupestris	Harpephyllum caffrum
Anastrabe integerrima	Ipomoea sagittata
Apodytes dimidiata subsp. dimidiata	Kalanchoe rotundifolia
Aristea ecklonii	Memecylon natalense
Asparagus macowanii	Millettia grandis
Behnia reticulate	Ochna arborea var. arborea
Bulbophyllum scaberulum	Olea capensis subsp. enervis
Burchellia bubalina	Panicum deustum
Cheilanthes viridis var. macrophylla	Plectranthus fruiticosus
Clivia gardenia	Plectranthus hadiensis var. tomentosus
Cotyledon orbiculata	Protorhus longifolia
Crassula perfoliata var. heterotricha	Psydrax obovata subsp. obovata
Croton sylvaticus	Rhipsalis baccifera
Cryptocarya wyliei	Rhoicissus tomentosa
Cyanotis speciosa	Robsonodendron eucleiforme
Cyperus albostriatus	Scilla sp.
Cyperus rupestris	Searsia chirindensis
Cyrtorchis arcuata	Selaginella dregei
Dalbergia armata	Setaria megaphylla
Dietes butcheriana	Stenoglottis fimbriata
Dioscorea sylvatica	Streptocarpus wendlandii
Diospyros simii	Tarchonanthus trilobus var. trilobus
Dracaena aletriformis	Trema orientalis
Drimia elata	Tridactyle bicaudata

 Glossary

Anthesis – onset of flowering or the flowering period of a plant

Circumscissile – opening along a transverse line encircling the organ

Haustoria – the attachment of a parasitic plant to its host from which it obtains its water and nutrients

 

Acknowledgements

Roger Polhill for confirmation of the identification of A. wyliei.  Prof. Braam van Wyk for his encouragement in carrying out field observations. Geoff Nichols and Dr. Hugh Chittenden for field assistance. Richard Boon for pushing me to publish.

References

BOON, R. (2010) Pooley’s trees of eastern South Africa. A complete guide. Flora and Fauna Publications Trust, Durban, 626 pp. 

DANIELS, F. (2005) Actinanthella wyliei (Sprague) Wiens. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2021/05/31

POLHILL, R. M. & WIENS, D. (1998) Mistletoes of Africa. The Royal Botanic Gardens, Kew, pp. 99–100.

About the author: Sharon is Ezemvelo KZN Wildlife’s District Ecologist Central East, based in Mtunzini and is responsible for the King Cetshwayo and iLembe Municipal Districts. Part of the Ecological Advice East Division, Sharon provides ecological advice support to Protected Area and District Conservation Managers, co-ordinates and manages several monitoring programmes and is an Environmental Management Inspector (EMI-Level 2). Sharon is passionate about her work, has a wide range of interests, including plants and animals and how they fit into their habitats.