Erithalis fruticosa is common locally and across the range of the genus, and is morphologically quite variable. It characteristically grows in seasonal habitats and/or in areas of edaphic water stress on limestone pavements and beaches. The plants range from small bushes to trees up to 8 m tall, and the leaf, inflorescence, and flower sizes vary. 

The circumsrciption of Erithalis fruticosa in relation to Erithalis odorifera is problematic, and the evidence available is not adequate to understand their systematics and most authors have resolved this taxonomy in their own various ways. Negrón-Ortiz (2005) and Howard (1989) separated these species, and they are separated here geneally following Howard: most plants of this complex belong to Erithalis fruticosa, but particularly robust and fragrant plants of the Lesser Antilles are here included in Erithalis odorifera. The name Erithalis odorifera has been included by various other authors within the circumscription of Erithalis fruticosa based on different considerations, including the number of plants that clearly are intermediate in form (e.g., Steyermark, 1974); field observations that find only one species in a region where two have been reported (e.g., Adams 1975); and inaccurate characters used to separate these, such as supposedly fragrant vs. non-fragrant flowers while all the plants have some fragrance. The limited molecular analysis of Negrón-Ortiz & Watson (2002) found the plants of the Lesser Antilles and Puerto Rico that they included in Erithalis odorifera grouped together, and this clade placed sister to a clade with four other species, three of which are limited in range. The plant from the Bahamas they included here in Erithalis odorifera was not grouped with the other samples of this species, and this result agrees with the treatment here of Erithalis odorifera to include only robust plants with relatively large flowers from the Lesser Antilles and eastern Greater Antilles. (The molecular analysis of Paudyal et al., 2018, included only one sample per Erithalis species and shed sno light on this particular species delimitation question.) The robust morphological form and biogeographically distinct distribution of Erithalis odorifera as it is circumscribed here could correspond with a robust form that arises in relatively wetter ecosystems, and/or a biogeographically localized population, rather than distinct species, although the molecular results of Negrón-Ortiz and Watson suggest there may be two lineages here. The plants are provisionally separated here based on the occurrence of several Rubiaceae species in the Antilles that are distinct in life but often impossible to distinguish as herbarium specimens (e.g., Palicourea crocea and Palicourea croceoides). As noted by Negrón-Ortiz, much more work including field study is needed to clarify the systematics and biogeography of these plants. These two species seem to both be present and widely distributed in Puerto Rico, and this island would be a key area for field work. 

Erithalis fruticosa was documented in field observations by Negrón-Ortiz (2005) as having variation in fruit color within a region and within populations in the Bahamas and southern Florida, variously purple-black or white flushed with pink.