How to change legend key shape for ggtree

I am working with a ggtree plot. Data used is available here and you can pull the phylo tree directly from ggtree.

Load required packages

#load libraries
pacman::p_load(
          here,
                    dplyr,
                    googlesheets4, 
                    tidyverse, 
                    rotl, 
                    dplyr, 
                    ape, 
                    ggplot2, 
                    ggnewscale, 
                    ggtree, 
                    ggtreeExtra,
                    taxize,
                    rentrez
)

Import data

data_for_tree_plot <- read.csv(here("data", "data_for_tree_plot.csv")) #data is available through link above
nwk <- system.file("extdata", "sample.nwk", package="treeio")
mytree <- groupClade(read.tree(nwk), c(17, 21))

Build phylogenetic tree

p <- ggtree(mytree, layout = "circular", lwd = 0.75, aes(colour=species_class))
p <- p %<+% data_for_tree_plot + # link plot to data
  scale_colour_manual(values = c("#EE3377", "#332288", "#EECC66", "#6699CC", "#EE7733", "#882255"), #colours for taxa
      name="Class", 
      breaks=c( "Arachnida", "Insecta", "Actinopterygii", "Mammalia", "Reptilia", "Aves"))
p # Circular tree

This gives me this plot.

This is fine. However, I would like to change the legend key so that it looks like this instead.

I have tried changing the legend.key fill, but this changes all the fills instead of one fill at the time. I have also tried theguide_legend(override.aes, but this also does nothing.

Does anyone know how to change the legend key shapes for ggtree objects?

If you have an up-to-date version of ggplot, you can use the key_glyph parameter to change the glyph.

Using some example data from ggtree (sorry, I'm not going to download all that):

library(ggtree)

nwk <- system.file("extdata", "sample.nwk", package="treeio")
tree2 <- groupClade(read.tree(nwk), c(17, 21))

ggtree(tree2, aes(color=group), key_glyph = 'rect')

Now, normally, we would pass key_glyph = "rect" to the relevant geom (and we could do that here with geom_tree(key_glyph = 'rect')), but it seems that ggtree passes any ... arguments to the geom (the documentation doesn't specify this, ggtree can be a bit odd at times).