[17] The term 'stramenopile' sought to identify a clade (monophyletic and holophyletic lineage) using the approach developed by transformed cladists of pointing to a defining innovative characteristic or apomorphy.

[18] Over time, the scope of application has changed, especially when in the 1970s ultrastructural studies revealed greater diversity among the algae with chromoplasts (chlorophylls a and c) than had previously been recognized.

One consequence was that an array of heterotrophic organisms, many not previously considered as 'heterokonts', were seen as related to the 'core heterokonts' (those having anterior flagella with stiff hairs).

Rather than continue to use a name whose meaning had changed over time and was hence ambiguous, the name 'stramenopile' was introduced to refer to the clade of protists that had tripartite stiff (usually flagellar) hairs and all their descendants.

[20] The proteins that code for the mastigonemes appear to be exclusive to the stramenopile clade, and are present even in taxa (such as diatoms) that no longer have such hairs.

There is a transitional helix inside the flagellum where the beating axoneme with its distinctive geometric pattern of nine peripheral couplets around two central microtubules changes into the nine-triplet structure of the basal body.

[30] The brown algae, including familiar seaweeds like wrack and kelp, are major autotrophs of the intertidal and subtidal marine habitats.

[31] Some of the bacterivorous stramenopiles, such as Cafeteria, are common and widespread consumers of bacteria, and thus play a major role in recycling carbon and nutrients within microbial food webs.

[36] In addition, species of Telonemia, the sister group to SAR, exhibit heterokont flagella with tripartite mastigonemes, implying a more ancient origin of stramenopile characteristics.

[39][40] In addition, a flagellate species discovered in 2023, Kaonashia insperata, remains in an uncertain phylogenetic position, but more closely related to Gyrista than to other clades.

[41] Platysulcus Labyrinthulomycetes Eogyrea Placididea Nanomonadea Opalinata Bicosoecida Developea Pirsonea Hyphochytriomycetes Oomycetes Ochrophyta (=Heterokontophyta) Kaonashia The classification of the stramenopiles according to Adl et al. (2019), with additions from newer research:[43] [4]