Two commits since v2.9.1, no migration:

- #410 a root species now claims its plant (plants.main_species_id), and
  Migrators::PlantMainSpeciesWorker backfills the 52,601 plants that had
  none. GET /api/v1/plants/:id rendered main_species, image_url, year and
  bibliography as null for those.
- #411 the name validator accepts the spaced nothogenus sign
  ("× Agropogon lutosus"), which no rank accepted before.