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Most spp.of the genus Cassytha (Lauraceae) occur in Australia, with two outlying spp. occurring in southern Africa.
In and near Fitzgerald River National Park (FRNP, https://breaking-the-borders.com/en/fitzgerald-river-national-park/), Western Australia, there are six spp. of Cassytha - probably the greatest diversity of perennial parasitic lianes on Earth.
Strands of various spp. of Cassytha can be found from ground level to 7 m high.
Although all have indehiscent, potentially edible fruits of common design, the size of the fruits varies considerably. Some (particularly Cassytha micrantha and Cassytha glabella) are too small to be considered fleshy fruits, and are probably dispersed and sown by ants.
This means that Cassytha is yet another of the many genera of 'plasticfruits' (https://www.inaturalist.org/journal/milewski/61996-plasticfruits-part-1-how-an-ordinary-daisy-becomes-extraordinarily-fruity#), which stretch, within a given genus, from vertebrate-dispersed to non vertebrate-dispersed spp.
Despite their diversity in/near FRNP, all forms of Cassytha are absent from calcareous sand hereabouts, except where limestone crops out, and where Eucalyptus forms dense stands.
In this region, stands of vegetation richest in lianes are the ones poorest in Cassytha, suggesting that this parasitic genus is suited to sites and strata prohibitive to other types of lianes.
The littoral dune of calcareous sand in/near FRNP, vegetated patchily by e.g. Acacia rostellifera, Melaleuca lanceolata, and Chenopodium spp., is free of Cassytha and virtually free of other parasites (whether before or after fire) despite the favourable content of phosphorus in the sand, and Cassytha was also absent from woodland of Eucalyptus occidentalis, containing Santalum on alluvium (visited in November 1991).
Cassytha melantha (https://www.inaturalist.org/taxa/733735-Cassytha-melantha)
https://www.inaturalist.org/observations/17702842
https://www.inaturalist.org/observations/70183424 and https://www.inaturalist.org/observations/108575414 and https://www.inaturalist.org/observations/103295193 and https://www.inaturalist.org/observations/71931219
fruit dull orange-hued, diam. 0.85 cm, seed diam.0.5 cm; fruit mass >0.3 g.
Cassytha pomiformis (https://www.inaturalist.org/taxa/851596-Cassytha-pomiformis)
I observed this species in ?Banksia kwongan on deep siliceous sand (certainly SS 1 type) in/near FRNP
no photo available of fruit, which is larger than that of C. glabella
fruit oblong, hairy, fleshy, dull-hued, yellow-green-black, 1.0 X 0.6 cm
Cassytha racemosa (https://www.inaturalist.org/taxa/800963-Cassytha-racemosa)
no photo available of fruit
fruit not necessarily fleshy
fruit oval, ribbed, dull-hued, 0.7 X 0.5 cm
fruit size similar to that of C. glabella
fruit size according to literature: diam.0.4 cm (Weber 1981), 1.0 X 0.4 cm (another ref.)
Cassytha glabella (https://www.inaturalist.org/taxa/323804-Cassytha-glabella)
https://www.inaturalist.org/observations/129653032 and https://www.inaturalist.org/observations/135894298 and https://www.inaturalist.org/observations/132378556 and https://www.inaturalist.org/observations/130206723
fruit small, variable in shape, greenish or dull orange-hued, meagre-fleshy but succulent (verified by me in FRNP, Nov. 1991), 0.4 X 0.2 cm to 1.1 X 0.3 cm, seed diam. 2.5 mm. Another of my field-notes states fruit dimensions average 0.65 X 0.25 cm, but as little as 0.5 X 0.15 cm, and as much as 1.1 X 0.4 cm.
Cassytha flava (https://www.inaturalist.org/taxa/851590-Cassytha-flava)
restricted to kwongan on sandplain
no photo available of fruits
fruit small, inconspicuous, greyish, hairy, 0.5 X 0.4 cm
Cassytha micrantha (https://www.inaturalist.org/taxa/745928-Cassytha-micrantha)
no photo available of fruit
fruit extremely small, inconspicuous, 0.3 X 0.2 cm
SUCCESSIONAL STATUS
Although all its habitats in/near FRNP are subject to fire, Cassytha shows little relationship to fires. It regenerates germinatively, in some spp. possibly from hard, long-lived seed sown before the fire (Weber 1981, Fox 1988).
Although Cassytha (pomiformis?) appears as sparse populations of semi-prostate, dark plants in the early regeneration on open, burnt ground (some stands extending 2 m across bare spaces), it is not particularly prolific at this stage (percent foliage cover <0.1% in regeneration on siliceous sand (SS1 type), two years or less after intense fire) and does not behave as a fireweed, although it does promptly regenerate germinatively.
Any parasite is limited by the regeneration of its hosts and, at least on deep siliceous sands and quartzite alluvium, the hemiparasitic Nuytsia floribunda (https://www.inaturalist.org/observations/104204182) is a very rapid, vegetative regenerator after fire, limiting the opportunities for Cassytha at this stage.
Casytha glabella tends simply to maintain small but significant contribution to the foliage cover of the stand, through the cycle of fire and regeneration.
Cassytha micrantha re-establishes from seedlings within 2 y of fire (Newbey 1987), whereas C. melantha does not for at least two years (Newbey 1987). This difference can most parsimoniously be explained by the speed of regeneration of different strata and life-forms of hosts.
Where the marlocks (https://en.wikipedia.org/wiki/Marlock) favoured by C. melantha are killed by fire, the flush of pauciennial Alyogyne (https://www.inaturalist.org/observations?place_id=6827&taxon_id=71957&view=species) and Kennedia (https://www.inaturalist.org/observations?place_id=6827&taxon_id=71957&view=species) dominating the regeneration stands in the first few years after fire is free of this and all other parasites.
Cassytha does not appear to parasitise Nuytsia floribunda. This is true despite the two types of parasites coexisting, and mistletoes being known to parasitise other parasites, including other mistletoes.
PHENOLOGY
All spp. of Cassytha in/near FRNP flower in spring. However, C. melantha finishes in October (Newbey 1987, pers. obs. 1991), whereas other spp. start in Oct.-Nov. and extend to January.
Cassytha glabella may have a particularly protracted flowering season (Newbey 1987), and was seen in fruit in/near FRNP in mid-November 1991 and late April 1992.
Cassytha cannot be considered an autumn fruiter, as are so many bird-dispersed plants of the temperate zone, including Syzygium, Punica, Crataegus/Cotoneaster, Carissa, and Psidium, all fruiting in May 1997 in Claremont-Newlands-Rondebosch, in Cape Town, as I analysed these field-notes.
DETAILED ACCOUNT OF SEVERAL SPECIES
Cassytha melantha:
See https://www.yarraranges.vic.gov.au/PlantDirectory/Climbers-Creepers/Cassytha-melantha
In/near FRNP, this species occurs in yate and mallee of Eucalyptus gardneri, in gorges,and on alluvia and coastal dunes. Its habitat tends to be base-rich. It occurs also in moort forest (Eucalyptus platypus).
Cassytha melantha forms the most substantial foliage (strand diameter 2 mm) and fleshy fruit found in this genus in or near FRNP.
Although the fruit does not seem to ripen to a bright hue or a sweet taste, it is too large to be moved far by ants, is not prone to dropping to the ground, and has a somewhat vis ours coating around the seed, suggesting dispersal by birds.
Cassytha melantha parasitises the canopy of tall, mature plants of Eucalyptus on relatively phosphorus-rich soils (where it may exceed 1% foliage cover in some stands). It is absent from oligotrophic landforms, even where Eucalyptus is abundant and reaches 4 m high, such as in mallee-heath in and near FRNP.
This species replaces mistletoes, which are virtually absent from south coastal Western Australia.
Like other parasites, it apparently benefits from physical disturbance of the stands of its hosts. It tends to be common only at the edges of stands of tall eucalypts. It was absent from the stands I examined of Eucalyptus occidentalis on alluvial levees of drainage lines. However, it was present in a stand of the same species at the disturbed edges of a swamp of paperbark Melaleuca.
The fleshy fruit of C. melantha is approximately similar in size to those of its host, Eucalyptus platypus (https://www.inaturalist.org/taxa/201389-Eucalyptus-platypus), as well as the mistletoes it apparently replaces in vegetation subject to canopy-wildfires.
Cassytha racemosa:
Cassytha racemosa is similar in the size and height of the plant, and in the size of the fruit, to Cassytha glabella. It does not contain alkaloids. It flowers in spring, as I noted in Nov.1991 in/near FRNP, and at Sheepwash Creek much farther to the west. It is well into its flowering season in November (pets. obs.; Newbey 1987), but was not fruiting in late Nov. 1991.
In/near FRNP, this species is recorded from coastal dunes, and RMC plots on laterite and limestone, but not in moort (Eucalyptus platypus) or Eucalyptus gardneri. However, in another table (?in Newbey 1987), it is listed from yate, Agonis, Eucalyptus angulosa, Eucalyptus pleurocarpa, thicket, and heath. It is possibly restricted to mature stands of vegetation.
This species may have relatively restricted occurrence in/near FRNP (Newbey 1987). However, I observed this or a similar form in Upland environments (where unrecorded by Newbey 1987), as well as on coastal dunes where a heath stratum was present.
Cassytha glabella:
This species is even more widespread than C. melantha (Weber 1981, Fox 1988). In/near FRNP it occurs in most habitats. It is typical of Eucalyptus pleurocarpa mallee-heath, and found in most other vegetation types including kwongan on siliceous sand (SS1 type) and RMC limestone type. However, it does not occur in Eucalyptus platypus forest.
Cassytha glabella favours Myrtaceae as hosts. In/near FRNP, it forms relatively small plants in low, small-leafed shrubs, often of Melaleuca, in the heath stratum, on oligotrophic soils.
Cassytha glabella flowers in summer. It produces its First fruits at the same time as its larger congener, C. melantha (e.g. late Nov. 1991, and I have a field-note stating end of April 1982, in mallee-heath, where the plant is fine-stranded and yellow). However, it tends not to coexist in the same stands as C. melantha, owing to ecological differences.
This species may be dispersed by small birds (e.g. Zosterops, see notes from Ian Rooke), but appears equally suitable for ants. Did Berg (1975) record it?
Both C. glabella and C. melantha have fruit-pulp that tastes rather resinous, possibly because of the 'resin' content of the Myrtaceae they parasitise.
Habitat differences between C. glabella and C. racemosa are unclear. The latter has fruits of similar size, and parasitises similar hosts, but apparently starts fruiting later in the season.
Cassytha micrantha:
See https://florabase.dpaw.wa.gov.au/browse/profile/2954
Cassytha micrantha is restricted to coastal southwestern Australia. Nowhere is it common.
In/near FRNP, it occurs on plains, in Eucalyptus pleurocarpa mallee-heath, in kwongan on siliceous sand (SS1 type), in RMC laterite plot, and in RMC limestone plot.
Cassytha micrantha is an extremely gracile, low-growing plant, tending to parasitise wiry sedge-like plants.
Brown and Hopkins (1983) recorded C. micrantha in kwongan in Tutanning Nature Reserve (https://www.pingelly.wa.gov.au/Profiles/pingelly/Assets/ClientData/Tutanning_Hut_-_Brochure.pdf), on laterite, sand and duplex substrate (sand over clay).
Cassytha micrantha flowers in summer, by mid- to late November (pers. obs., 1991; Newbey 1987), and started to fruit late in November (pers. obs. South Stirling, 1982).
COMPARISON OF FRUITS WITH SOUTHERN AFRICA
In the Cape Flora of southern Africa, the only species of Cassytha is Cassytha ciliolata (https://www.inaturalist.org/taxa/461729-Cassytha-ciliolata). The fruits have diameter about 0.5 cm, which is not particularly large. However, the succulent fruits turn red, making them brighter-hued than any of the Australian spp. discussed here.
Cassytha pubescens (https://www.inaturalist.org/taxa/323806-Cassytha-pubescens) does not occur in/near Fitzgerald River National Park. However, it occurs under the mediterranean-type climate in South Australia, making it ecologically as comparable with Cassytha ciliolata of South Africa as are any of the spp. in/near FRNP.
Cassytha pubescens flowers in summer-autumn (Forde 1986).Its fruit has diameter 0.5-0.6 cm (data presumably from Weber 1981), which is larger than that of e.g. Cassytha glabella. However, based on dimensions given in Wikipedia, the fruit of C. pubescens is probably also larger than that of Cassytha ciliolata.
For the relative sizes, please see https://www.inaturalist.org/observations/101518388 vs https://www.inaturalist.org/observations/141352431.
The fruit of C. pubescens is greenish/reddish/black (Forde 1986). It is eaten by e.g. Dasyornis broadbenti (https://www.inaturalist.org/taxa/13481-Dasyornis-broadbenti), Gavicalis virescens (https://www.inaturalist.org/taxa/370319-Gavicalis-virescens), and Acanthagenys rufogularis (https://www.inaturalist.org/taxa/12677-Acanthagenys-rufogularis).
(This species does not contain alkaloids.)
Observations in iNaturalist show that the hues of the ripe fruit are subtle, rather than bright:
https://www.inaturalist.org/observations/142334620https://www.inaturalist.org/observations/139208240
https://www.inaturalist.org/observations/113690097
https://www.inaturalist.org/observations/96920708
https://www.inaturalist.org/observations/74836936
https://www.inaturalist.org/observations/62997915https://www.inaturalist.org/observations/60804559
https://www.inaturalist.org/observations/39962834
What emerges is that, although C. pubescens of southern Australia and C. ciliolata of southernmost South Africa are intercontinental counterparts, there is a difference in the conspicuousness of the ripe fruits. Although C. pubescens has the advantage of size, the red is so bright in C. ciliolata that its minimum brightness exceeds the maximum brightness of C. pubescens.
Ripe fruits of Cassytha ciliolata:
https://www.inaturalist.org/observations/141975744
https://www.inaturalist.org/observations/141438858
https://www.inaturalist.org/observations/136452822
https://www.inaturalist.org/observations/101345430
DISCUSSION
Many naturalists are familiar with Cassytha, particularly in the Cape Floristic region of South Africa.
However, many may not realise that
- this genus represents an intercontinental pattern similar to the better-known pattern in Proteaceae, and
- the bright red hue of the ripe fruits of the species in fynbos, namely C. ciliolata, is odd in the genus, which otherwise has fairly dull-hued fruits, some of them probably dispersed by ants rather than birds.
