Plants in this family have simple, opposite,decussatedleaves with entire (or sometimes toothed, lobed, or spiny) margins, and withoutstipules. The leaves may containcystoliths,calcium carbonate concretions, seen as streaks on the surface.
Theflowers are perfect,zygomorphic to nearlyactinomorphic, and arranged in aninflorescence that is either aspike,raceme, orcyme. Typically, a colorfulbract subtends each flower; in some species, the bract is large and showy. Thecalyx usually has four or five lobes; thecorolla tubular, two-lipped or five-lobed;stamens number either two or four, arranged in pairs and inserted on the corolla, and theovary is superior and bicarpellated, with axileplacentation.
Thefruit is a two-celledcapsule,dehiscing somewhat explosively. In most species, theseeds are attached to a small, hooked stalk (a modifiedfuniculus called ajaculator or a retinaculum) that ejects them from the capsule. This trait is shared by all members of the cladeAcanthoideae. A 1995 study of seed expulsion in Acanthaceae used high speed video pictures to show that retinacula propel seeds away from the parent plant when the fruits dehisce, thereby helping the plant gain maximumseed dispersal range.[3]
Since the first comprehensive classification of Acanthaceae in 1847 byNees,[8] there have been a few major revisions presented since for the whole family.
Lindau, in 1895, divided the family into the subfamilies Mendoncioideae,Thunbergioideae,Nelsonioideae, andAcanthoideae.[9] Critically, Mendoncioideae, Thunbergioideae, and Nelsonioideae do not possess retinaculate fruits—and it is this distinction, between classifying Acanthaceae into a family that includes those clades with non-retinaculate fruits and one that excludes them, that still persists to the modern day.
Bremekamp, in 1965, presented a classification of Acanthaceae that differed from that of Lindau, for his Acanthaceae excluded genera that lack retinaculate fruits.[10] He placed Nelsonioideae withinScrophulariaceae, classified Thunbergiaceae and Mendonciaceae as distinct families and divided his Acanthaceae into two groups (Acanthoideae and Ruelloideae) based on the presence or absence ofcystoliths, articulatestems, monothecateanthers, and colpatepollen.
In Scotland and Vollesen's 2000 study,[11] they accepted 221genera and detailed five major groups within Acanthaceae s.s. (that is, those possessing retinaculate fruits), which is equivalent to Acanthoideae Link sensu Lindau 1895. Out of those 221 genera, they placed 201 of them into seven infrafamilial taxa of Acanthaceae, leaving only 20 unplaced.
In the current understanding of Acanthaceae, Acanthaceaes.s. includes only thoseclades with retinaculate fruits (that is,Acantheae,Barlerieae,Andrographideae, Whitfieldeae,Ruellieae, and Justiceae), while Acanthaceaes.l. includes those clades as well as Thunbergioideae, Nelsonioideae, andAvicennia.[12]
Much research, using both molecular data andfossils, has been conducted in recent years regarding the dating and distribution of the Acanthaceae andLamiales lineage, although there still remains some ambiguity.
In a 2004 study on the molecular phylogenetic dating of asterid flowering plants, researchers estimated 106 million years (MY) for the stem lineage of Lamiales, 67 MY for the stem lineage of Acanthaceae, and 54 MY for thecrown node of Acanthaceae (that is, the age of extant lineages with the family).[13] These estimates are older than those based on fossils that can confidently be assigned to Lamiales, which are middleEocene in age, ca. 48-37 MY.[14]Palynomorphs that definitively show the existence of Acanthaceae are known from the upperMiocene, with the oldest ca. 22 MY.[15]
^abAwan, A.J., Aslam, M.S. (2014). "FAMILY ACANTHACEAE AND GENUS APHELANDRA: ETHNOPHARMACOLOGICAL AND PHYTOCHEMICAL REVIEW".International Journal of Pharmacy and Pharmaceutical Sciences.6 (10):44–55.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Wostmann, R; Liebezeit, G (2008). "Chemical composition of the mangrove holly Acanthus ilicifolius (Acanthaceae)—review and additional data".Senckenbergiana Maritima.38:31–37.doi:10.1007/bf03043866.S2CID38592501.
^Tripp, E. A.; Daniel, T. F.; Fatimah, S.; McDade, L. A. (2013). "Phylogenetic Relationships within Ruellieae (Acanthaceae) and a Revised Classification".International Journal of Plant Sciences.174 (1):97–137.doi:10.1086/668248.S2CID84423889.
^Wortley, A.H., Harris, D.J. & Scotland, R.W.; Harris, D. J.; Scotland, R. W. (2007). "On the Taxonomy and Phylogenetic Position of Thomandersia".Systematic Botany.32 (2):415–444.doi:10.1600/036364407781179716.S2CID85726050.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Schwarzbach, Andrea E.; McDade, Lucinda A. (2002). "Phylogenetic relationships of the mangrove familyAvicenniaceae based on chloroplast and nuclear ribosomal DNA sequences".Systematic Botany.27 (1):84–98.doi:10.1043/0363-6445-27.1.84 (inactive 11 July 2025).JSTOR3093897.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
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