The parasitic liane Cassytha in southwestern Australia and an ecologically similar region of southern Africa

@alan_dandie @michaelcincotta @insiderelic @scottwgavins @cobaltducks @tonyrebelo @botaneek @troos @fynbosphil @fynbosfia @fynbossie @fynbosfriend @fynbosfae @graham_g @jeremygilmore @arthur_chapman @peterslingsby @benjamin_walton @jayhorn

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.
Posted by milewski milewski, November 24, 2022 07:11

Comments

Cassytha filiformis (https://www.inaturalist.org/taxa/160172-Cassytha-filiformis and https://bie.ala.org.au/species/https://id.biodiversity.org.au/node/apni/2910118) is pantropical.

In Western Australia, it may perhaps occur east of FRNP (https://www.inaturalist.org/observations/60270940.)

This species has small fruits (4-8 X 3-5 mm), larger than those of Cassytha glabella. When ripe they are usually whitish (https://www.inaturalist.org/observations/124292187) and sweetish.

If this species occurs in/near FRNP, this would bring the number of spp. of Cassytha here up to seven.

Posted by milewski 11 days ago (Flag)

"with two outlying spp. occurring in southern Africa"
https://www.inaturalist.org/observations?place_id=113055&taxon_id=119899&view=species
3 species: Cape Flora ! Pondoland ! Global tropics.

Posted by tonyrebelo 8 days ago (Flag)

@tonyrebelo @jeremygilmore @alan_dandie @peterslingsby

The biogeography of Cassytha can be summarised as follows, based on observations in iNaturalist:
Restricted to Australia 13 spp.
Restricted to Australia and New Zealand 2 spp.
Restricted to southern Africa 2 spp.
Tropicopolitan 1 sp.

Hence, discounting the tropicopolitan species, the intercontinental asymmetry is Australia 15 spp., southern Africa 2 spp.

In the areas most closely matched for climate (mediterranean-type) and soils (nutrient-poor), viz Fitzgerald River National Park and the Agulhas Plain, the intercontinental asymmetry is 6 spp. vs 1 sp.

And a surprising finding is that none of the Australian spp. really emulates the fynbos sp., Cassytha ciliolata, in being unambivalently bird-dispersed, based on the consistently bright red hue of the diaspore.

This in turn seems to correlate with the observation that southwestern Australia lacks any counterparts for Pycnonotus and Colius, w.r.t. degree of specialisation on fleshy fruits.

Overall, the closest match in Australia for C. ciliolata + pondoensis is C. glabella (https://www.inaturalist.org/taxa/323804-Cassytha-glabella). The fruits of this species do stretch to reddish, but they retain an oblong shape and a handle at the distal end, seemingly suitable for ants (https://www.inaturalist.org/observations/92570804).

@alan_dandie Dear Alan, have you observed whether the fruits of C. glabella tend to fall to the ground when ripe? If not, are they attached loosely enough that fairly large ants, e.g. Iridomyrmex, could detach them after climbing the plants?

Posted by milewski 8 days ago (Flag)
Posted by milewski 8 days ago (Flag)

Cassytha ciliolata germinates on branches and attaches haustoria to stems. Presumably if dropped on the ground they attach to nearby stems (and if deposited on rocks, and rocky perches they try attaching to rocks and die). How do species buried in ants nests establish? Either they must initially attach to roots, or alternatively they need a non-parasitic stage to reach stems to attach to ....
(However, once established Cassytha seem to spread extensively by growth).

Posted by tonyrebelo 7 days ago (Flag)

@tonyrebelo

Do you have a reference for epiphytic germination in Cassytha ciliolata?

As far as I know, Cassytha germinates terrestrially and photosynthesises until it reaches a host.

In the case of Cassytha filiformis (https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pd-42.pdf), the seedlings are said to be able to grow for two months, reaching 30 cm long, before attaching to a host. The pantropical distribution of this species indicates dispersal partly by inanimate means, which also implies germination in beach sand after the seeds wash up.

Cuscuta, which belongs to a different family and is annual, has a similar growth-form and nutritional mode. It lacks zoochory, and is thus unlikely to germinate epiphytically.

Cassytha melantha, which parasitises eucalypts, has a large diaspore for its genus. I suppose that the seed is large enough to subsidise germination vigorous enough for the seedling to climb several metres, to the nearest available foliage.

So, unless you know of a particular study to the contrary, can we assume that all spp. of Cassytha germinate terrestrially?

Posted by milewski 7 days ago (Flag)

According to Parasitic Plants of southern Africa, the fruit is a hard nut that does not germinate after bird dispersal for several years (until after fire??).
The seeds I have been observing germinating must therefore have been Viscum and not Cassytha.

Sorry about that.

Hard to believe though that Cassytha seeds dropped by birds on the ground dont just get eaten by rodents. Or burned in the next fire. Something still missing in the story.

Posted by tonyrebelo 7 days ago (Flag)

@tonyrebelo

Here is a paper confirming dormancy in the seeds of Cassytha, even in the case of the 'weedy' C. filiformis, which one does not expect to have any particular relationship to fire: https://www.publish.csiro.au/bt/bt12275 and
https://www.researchgate.net/profile/K-Jayasuriya/publication/237150836_Water-impermeable_fruits_of_the_parasitic_angiosperm_Cassytha_filiformis_Lauraceae_Confirmation_of_physical_dormancy_in_Magnoliidae_and_evolutionary_considerations/links/56a0508708ae2c638eb7f781/Water-impermeable-fruits-of-the-parasitic-angiosperm-Cassytha-filiformis-Lauraceae-Confirmation-of-physical-dormancy-in-Magnoliidae-and-evolutionary-considerations.pdf

However, this abstract is misleading in describing the 'fruit' as having a water content of 10-16%. The ripe fruits look succulent to me (https://www.inaturalist.org/observations/3995762 and https://www.inaturalist.org/observations/31164149 and https://www.inaturalist.org/observations/75380727 and https://www.inaturalist.org/observations/141172144 and https://www.inaturalist.org/observations/124292187 and https://www.inaturalist.org/observations/111203389), which would mean that the water content of the fruit-pulp is >80%.

Here is confirmation that the fruit-pulp of C. filiformis is succulent:
https://brill.com/view/journals/ijps/28/1/article-p44_4.xml
https://www.tandfonline.com/doi/abs/10.1080/0021213X.1979.10676854

It is noteworthy that this part of the diaspore is actually derived from the calyx, not the carpels.

Here is a photo of the seeds of C. filiformis: https://www.inaturalist.org/observations/59199413.

Posted by milewski 7 days ago (Flag)

@tonyrebelo
The following is by far the best overall reference for all biological aspects of Cassytha filiformis: https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.11493

Posted by milewski 7 days ago (Flag)

@tonyrebelo @jeremygilmore

The following, of Cassytha filiformis, shows that the fruit-pulp is derived from the calyx. What would be the fruit-pulp in a drupe, namely the mesocarp, is incorporated into the dry, hard coating of the 'stone', which bestows seed-dormancy and recalcitrant germination.

https://www.researchgate.net/figure/a-Line-diagram-of-the-mature-fruit-and-b-a-detailed-drawing-of-fruit-seed-coat-of_fig4_237150836

Both Persea (avocado) and Cassytha belong to Lauraceae, but their fruits are different in anatomical derivation. The fruit of avocado is a single-seed berry, in which the fruit-pulp is the mesocarp. In Cassytha, the mesocarp has been incorporated into a 'stone', and a replacement for fleshy mesocarp has been configured from the calyx. This produces a fruit convergent with the drupe, because both the drupe and the fruit of Cassytha contain a 'stone'.

Posted by milewski 6 days ago (Flag)

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