Do succulent fruits extend to waterlogged sites in the Cape Floristic Region?

Succulent fruit-pulp, which contains more than 75% water when ripe, requires potassium for the maintenance of turgidity (https://www.pda.org.uk/nitrogen-potassium-interactions/#:~:text=Potassium%20is%20very%20important%20in,cells%2C%20causing%20them%20to%20swell.).

Hence we can expect plant species with succulent fruits to be absent from situations that are not conducive to a particular affluence of potassium relative to other nutrients (https://www.jstor.org/stable/2844617).

There are innumerable plant species with succulent fruits in the various indigenous floras of the world. There are also many domestic species bearing succulent fruits.

However, a pattern is evident: succulent fruits tend not to occur where the substrate is continually waterlogged. This limitation does not seem to have been overcome even by selective breeding in horticulture.

Waterlogging is known to inhibit the absorption by roots of potassium, to a greater extent than other nutrients (https://www.researchgate.net/profile/Sven-Schubert-2/publication/242710520_Water_logging_may_inhibit_plant_growth_primarily_by_nutrient_deficiency_rather_than_nutrient_toxicity/links/0f31752da8bdb7f765000000/Water-logging-may-inhibit-plant-growth-primarily-by-nutrient-deficiency-rather-than-nutrient-toxicity.pdf and https://www.publish.csiro.au/cp/cp09225 and https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.15751).

This is probably because, as has been known for at least 70 years, the absorption of potassium by roots particularly requires metabolic energy, but the anaeroby of waterlogging prevents the supply of oxygen to the roots (Page J B & Bodman G B, 1951, The effect of soil physical properties on nutrient availability, chapter 6, pages 133-166, in Mineral Nutrition of Plants, ed. by E Truog, The University of Wisconsin Press).

The above suggests that limitations on the affluence of potassium in waterlogged sites may tend to exclude species with succulent fruits.

Here I test this negative relationship by examining the occurrence of indigenous species with fleshy fruits in the Cape Floristic Region (https://en.wikipedia.org/wiki/Cape_Floristic_Region), relative to waterlogging.

Ilex mitis (https://www.inaturalist.org/taxa/133559-Ilex-mitis) seems to be anomalous relative to the pattern, because it has fleshy fruits and is particularly associated with wet sites.

This also applies to a lesser extent to Rapanea melanophloeos (https://www.inaturalist.org/taxa/578244-Rapanea-melanophloeos) and Myrsine africana (https://www.inaturalist.org/taxa/70260-Myrsine-africana), which both have fleshy fruits and are partly associated with wet sites. Rapanea melanophloeos is common where acidic streams reach the shore, producing deep seepage.

Halleria lucida (https://www.inaturalist.org/taxa/402272-Halleria-lucida) and Curtisia dentata (https://www.inaturalist.org/taxa/490221-Curtisia-dentata and https://www.inaturalist.org/observations/76983626) are also anomalous to some degree.

Morella serrata (https://www.inaturalist.org/taxa/492352-Morella-serrata) tolerates waterlogging.

Diospyros glabra (https://www.inaturalist.org/taxa/569146-Diospyros-glabra) is usually associated with well-drained sites, but extends to stream-beds (e.g. in Matjiesrivier Nature Reserve, https://www.trailforks.com/region/matjiesrivier-nature-reserve-37540/?activitytype=1&z=10.3&lat=-32.52797&lon=19.29449).

Asparagus spp. (e.g. https://www.inaturalist.org/observations/106741517) marginally tolerate waterlogging, but usually avoid wet sites.

Although waterlogging militates against succulence of fruit-pulp because it particularly inhibits the uptake of potassium, other factors are also involved in the overall affordability of potassium:

freedom from wildfire allows potassium in particular to be conserved in organic matter in the topsoil,
slow growth means that the demand for potassium in new foliage is limited, and
vegetative (as opposed to germinative) regeneration allows potassium to be conserved in woody burls and roots.

Most of the anomalous species pointed out above are indeed associated with wildfire-free vegetation or its edges. None has flammable foliage.

Rapanea melanophloeos and Halleria lucida grow relatively slowly and regenerate vegetatively, the latter species by means of a large burl. The fruit-pulp of H. lucida is unusually mucilaginous. In nearly 1100 observations of this species in iNaturalist I have seen no photo of a ripe fruit (https://www.inaturalist.org/observations?page=12&place_id=any&taxon_id=402272), suggesting that turgidity hardly needs to be maintained before the fruits are eaten by birds and the seeds are dispersed.

Myrsine africana is peculiar in seldom producing full-size fruits (https://www.inaturalist.org/observations/28046096). The fruit-pulp of Curtisia dentata seems to consist partly of air-pockets.

The fruit-pulp of Morella serrata is oily rather than succulent, so this species is not anomalous.

Ilex mitis seems to remain as the main anomaly.

However, this species: