Plasticfruits, part 2: Polygalaceae

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...continued from https://www.inaturalist.org/journal/milewski/61996-plasticfruits-part-1-how-an-ordinary-daisy-becomes-extraordinarily-fruity#.

In part 1, I described how evolutionarily plastic the fruits are in a mainly southern African genus (Osteospermum) of daisies (Asteraceae).

(Also, please see https://pza.sanbi.org/sites/default/files/info_library/fruits_fleshy_dry_pdf.pdf.)

The genus Muraltia (Polygalaceae) is geographically and ecologically similar to Osteospermum, despite belonging to an unrelated family (https://www.sciencedirect.com/science/article/abs/pii/S105579030600337X).

Like Osteospermum, Muraltia (https://en.wikipedia.org/wiki/Muraltia and http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&name=Muraltia_heisteria and https://cdn.environment.sa.gov.au/landscape/docs/hf/muraltia-heisteria-may-2019.pdf and http://pza.sanbi.org/muraltia-heisteria) contains wind-dispersed, ant-dispersed (https://www.jstor.org/stable/4621408 and https://www.jstor.org/stable/2260664) and vertebrate-dispersed species.

Although in both genera the seeds have food-bodies attached to them to attract ants, these take different forms.

In Osteospermum the food-body is the mesocarp that envelops the seed. By contrast, in Muraltia it is a handle-like edible attachment called an elaiosome (https://studylib.net/doc/8932239/elaiosomes-and-seed-dispersal-by-ants and https://en.wikipedia.org/wiki/Elaiosome).

The bright-hued fleshy fruits of Muraltia spinosa and Muraltia scoparia seem adapted for dispersal and sowing mainly by tortoises such as Chersina angulata (https://en.wikipedia.org/wiki/Angulate_tortoise). Unlike those of Osteospermum moniliferum, they remain crisp when ripe, and tend to fall to the ground.

Muraltia spinosa
https://www.ingentaconnect.com/content/aspt/sb/2006/00000031/00000003/art00009
http://pza.sanbi.org/muraltia-spinosa

Muraltia scoparia
http://pza.sanbi.org/muraltia-scoparia
https://www.inaturalist.org/taxa/590391-Muraltia-scoparia
https://www.inaturalist.org/observations/10974111

In the case of both Muraltia and Osteospermum, the species dispersed and sown by vertebrates were, for several decades, classified as separate genera, based on the form of the fruits (https://www.researchgate.net/publication/233494831_Evidence_for_Inclusion_of_South_African_Endemic_Nylandtia_in_Muraltia_Polygalaceae). This has since been corrected, with the taxonomic realisation that fruits are too adaptable to be reliable indicators of phylogenetic affinity.

Muraltia spinosa (https://www.inaturalist.org/taxa/526214-Muraltia-spinosa) is ecologically unusual, within the context of the Cape Floristic Region (https://en.wikipedia.org/wiki/Cape_Floristic_Region) and the Fynbos biome (https://en.wikipedia.org/wiki/Fynbos).

(Also see https://www.inaturalist.org/journal/milewski/72728-ecology-of-fleshy-fruits-in-oorlogskloof-nature-reserve-southwestern-cape-south-africa#.)

This is because M. spinosa shows an odd combination of

• succeeding in at least four different situations, viz. certain forms of renosterveld (on clay-rich soils on both shale and dolerite), marginally on certain forms of nama karoo (on dolerite), certain forms of fynbos (on coarse, deep sand), and certain forms of strandveld (on calcareous coastal sand),
• aphyllousness and retention of leaves,
• sclerophylly (in the form of photosynthetic stems) and fleshy fruits,
• semi-spinescence (in the form of the same photosynthetic stems) and tolerance of nutrient-poor soils with more-or-less flammable vegetation,
• semi-spinescence and evergreenness,
• succulent fruits and some tolerance to wildfire, and
• endozoochory and reptilian (rather than avian) agents of dispersal and sowing.

to be continued in https://www.inaturalist.org/posts/62307-plasticfruits-part-3-thymelaeaceae#...

Posted on February 19, 2022 02:09 AM by milewski