Boronia Sm.

Duretto, Marco F., Heslewood, Margaret M. & Bayly, Michael J., 2023, A molecular phylogeny of Boronia (Rutaceae): placement of enigmatic taxa and a revised infrageneric classification, Australian Systematic Botany 36 (2), pp. 81-106 : 101-102

Boronia Sm. , Tracts Nat. Hist. 288 (1798)

Type: Boronia pinnata Sm.

Perennial herbs, shrubs, rarely small trees; glabrous or with simple or stellate hairs. Leaves opposite, decussate, rarely in whorls of three (see series Boronella ), simple or imparipinnate or rarely bipinnate (see section Alatae ). Inflorescences axillary or terminal; flowers solitary or in cymes or pseudo-umbels or panicles, bisexual, 4-merous, rarely 5-merous ( B. scabra subsp. attenuata Paul G.Wilson ). Sepals free, open, imbricate or valvate, persistent or caducous. Petals free, imbricate or valvate, not obviously glandular; tip straight or with a subterminal apiculum on the abaxial surface; 1- or 3-veined at base; caducous or persistent. Stamens 8, rarely 4 of them caducous ( B. parviflora ); filaments usually inwardly curved, semiterete, glabrous or hairy, usually verrucose towards apex; anthers introrse, apiculate or not, connective usually inconspicuous or cream coloured, all or only antepetalous anthers fertile (see series Boronia and series Persistens ). Disc prominent, usually entire, rarely with antepetalous ( B. octandra ) or antesepalous ( B. tetrandra ) lobes. Carpels 4; ovaries free though united at apex on adaxial margin by the solitary style. Fruit of 1–4 basally connate follicles (cocci), dehiscing explosively ventrally with separating, elastic endocarp. Seed: sclerotesta smooth or minutely tuberculate, rarely prominently rugulose ( B. cymosa ), glossy or dull. (Adapted from Duretto et al. 2020).

An Australian (including Tasmania) and New Caledonian genus of 134 species classified into 10 sections, including 9 confined to Australia, and 1, section Boronella , to Grande Terre, New Caledonia. Two sections, Corynophyllae and Inornatae , are newly described, and a new combination at sectional level is made for section Ovatae . Novel infrasectional classifications are provided for sections Boronella , with two series, and Boronia , with four series. Sections Alatae , Imbricatae , Pedunculatae , apart from the addition of subspecies for B. denticulata Sm. ( Duretto 2019) , and Valvatae , apart from the addition of five species ( Barrett et al. 2015), remain as previously circumscribed by Duretto et al. (2013) and Bayly et al. (2015) and are not dealt with further here.

Key to the sections of Boronia

1. Branches, including cortex, strongly articulated at nodes; leaves verticillate in whorls of three, or opposite–decussate; cotyledons elliptic or suborbicular, wider than hypocotyl ( New Caledonia)........................................................section Boronella

Branches, including cortex, continuous (smooth) at nodes; leaves opposite–decussate; cotyledons linear, as wide as hypocotyl (Austr., Tas.)...............................................................................2

2. Petal aestivation known.................................................................3

Petal aestivation unknown...........................................................13

3. Petals valvate in bud......................................................................4

Petals imbricate in bud..................................................................7

4. Inflorescence axillary; stellate hairs present (sometimes only on flowers), rarely absent (Kimberley Region, WA), simple hairs also present (tropical, eastern and southern Austr.).................... ...........................................................................section Valvatae

Inflorescence terminal; all hairs simple (Southern Austr., Tas.)......5

5. Leaves simple..............................................section Corynophyllae

Leaves imparipinnate.....................................................................6

6. Inflorescence a many-flowered cymose panicle; peduncle present; leaves imparipinnate or bipinnate (SW Austr.)......section Alatae

Inflorescence cymose, 1(–3)-flowered; peduncle absent; leave imparipinnate (SE Austr.)....................................section Algidae

7. Leaves imparipinnate.....................................................................8

Leaves simple.................................................................................9

8. Inflorescence axillary, sometimes also terminal, 1–40+-flowered; stems smooth or glandular verrucose; staminal filaments glabrous or hairy.....................................................section Boronia

Inflorescence terminal, sometimes also terminal on short axillary branches, 1–3-flowered; stems glandular verrucose; staminal filaments glabrous...............................................section Inornatae

9. Seed rugulose; branches glabrous, developing a visible cream-coloured spongy layer with age.....................section Imbricatae

Seed smooth though sometimes minutely tuberculate; branches glabrous or hairy, not developing a visible cream-coloured spongy layer.............................................................................10

10. Seeds with a cream-coloured pulpy elaiosome at base; sepals valvate and usually caducous; branches glabrous or rarely woolly; inflorescence terminal, sometimes also upper axillary................. ...................................................................section Pedunculatae

Seeds without a basal elaiosome; sepals imbricate, persistent; branches glabrous or hairy; inflorescence terminal or axillary......11

11. Staminal filaments woolly–ciliate.................................................... ..............................................(section Boronia ) series Variabiles

Staminal filaments pilose, puberulous or glabrous......................12

12. Inflorescence axillary, 1–5-flowered, rarely in terminal cymes and then leaves broadly obovate to almost circular........................... ............................................................................section Boronia

Inflorescence in terminal and upper-axillary cymes, few to many-flowered; leaves narrowly oblong to oblong–elliptic or broadly ovate.....................................................................section Ovatae

13. Stellate hairs present (sometimes only on flowers), simple hairs also present; inflorescence axillary (N and SW WA, NT, Qld, NSW, Vic.)...................................................................section Valvatae

All hairs simple; inflorescence axillary or terminal (N and SW WA, Qld, NSW, Vic., Tas., SA).........................................................14

14. Leaves imparipinnate...................................................................15

Leaves simple...............................................................................19

15. Inflorescence axillary, sometimes also terminal..........................16

Inflorescence terminal, sometimes also terminal on short axillary branches....................................................................................17

16. Antepetalous anthers smaller than or equal to antesepalous anthers, if larger then branches hairy (southern Austr.)............................ ............................................................................section Boronia

Antepetalous anthers much larger than antesepalous anthers; branches glabrous (Kimberley Region, N WA)............................. ....................................(section Valvatae ) subsection Anomalae

17. Inflorescence a many-flowered cymose panicle; staminal filaments pilose; leaves imparipinnate or bipinnate.............section Alatae

Inflorescence cymose, 1–5-flowered; staminal filaments glabrous; leaves imparipinnate................................................................18

18. Stigma globular, much wider than style; leaves 3–9-foliolate; seed dull.......................................................................section Algidae

Stigma minute, as wide as style; leaves 3(5)-foliolate; seed shiny................................................................section Inornatae

19. Seed rugulose; branches glabrous, developing a visible cream-coloured spongy layer....................................section Imbricatae

Seed smooth though sometimes minutely tuberculate; branches glabrous or hairy, not developing a visible cream-coloured spongy layer.............................................................................20

20. Seeds with a cream-coloured pulpy elaiosome at base; sepals valvate, usually caducous; branches glabrous or rarely woolly; inflorescence terminal, sometimes also upper axillary.......section Pedunculatae

Seeds without a basal elaiosome; sepals imbricate, persistent; branches puberulous, pilose or glabrous; inflorescence terminal or axillary.................................................................................21

21. Leaves terete; inflorescence terminal; branches exfoliating and with a grey scurfy covering.............................section Corynophyllae

Leaves flat or terete, if terete then flowers axillary; branches various but not exfoliating or having a grey scurfy covering................22

22. Staminal filaments woolly–ciliate.................................................... .............................................[section Boronia ] series Variabiles

Staminal filaments puberulous, pilose or glabrous......................23

23. Inflorescence axillary, 1–5-flowered, rarely in terminal cymes and then leaves broadly obovate to almost circular......section Boronia

Inflorescence in terminal and upper-axillary cymes, few–many-flowered; leaves narrowly oblong to oblong–elliptic or broadly ovate.....................................................................section Ovatae