Salient features, floral diversity, diversity of families and phylogeny of the following orders: Tubiflorae and Helobieae

Salient features, floral diversity, diversity of families and phylogeny of the following orders: Tubiflorae and Helobieae:-

Tubiflorae:-

> Tubiflorae is a natural taxon. Plants are characterized by herbs with regular or irregular tetracyclic flowers, gamopetalous corolla, hypogynous and epipetalous stamens and unitegmic ovules.

> Tubiflorae is kept under the 7th series of Metachlamydeae by Engler & Prantl (1884- 1930). Its plants are grouped into 22 families. Further the Engler and Diels set up the order to contain eight sub-orders and 22 families, viz. 

i. Convolvulineae:- Convolvulaceae, Polemoniaceae, Fouqueriaceae

ii. Lennonineae:- Lennoaceae

iii. Boragineae:- Hydrophyllaceae, Boraginaceae

iv. Verbenineae:- Verbenaceae, Labiatae

v. Solanineae:- Nolanaceae, Solanaceae, Scrophulariaceae, Bignoniaceae, Pedaliaceae, Martyniaceae, Orobanchaceae, Gesneriaceae, Columelliaceae, Lentibulariaceae, Globulariacea

vi. Acanthineae:- Acanthaceae

vii. Myoporineae:- Myoporaceae

viii. Phrymineae:- Phrymaceae

> Tubiflorae of Wettstein has same circumscription as given by Engler (except that the Fouquieriaceae were placed in the Parietales and the Plantaginaceae were included here).

> Rendle supported Engler's circumscription, but the Convolvulaceae was segregated as the Convolvulales, the Fouqueriaceae and Lennoaceae omitted and the Selaginaceae created.

> Lawrence treated all the families in the order, but excluded the Columelliaceae.

> Hutchinson (1969) kept some of these families in Lignosae and Herbaceae within the different orders namely Bignoniales and Verbenales of Lignosae. Solanales, Personales, Boraginalesmand Lamiales are under herbaceae. Cronquist (1981, 1988) kept these families in the subclass Asteridae. Cronquist kept them in 3 orders viz., Solanales, Lamiales and Scrophulariales.

> Bentham and Hooker included these families in the Series Bicarpellatae under three orders as follows-

i. Polemoniales:- Polemoniaceae, Hydrophyllaceae, Boranginaceae, Convolvulaceae and Solanaceae.

ii. Personales:- Scrophulariaceae, Orobanchaceae, Lentibulariaceae, Columelliaceae, Gesneriaceae, Bignoniaceae, Pedaliaceae and Acanthaceae.

iii. Lamiales:- Myoporineae, Selagineae, Verbenaceae and Labiatae.

> The taxon Tubiflorae possesses several illustrating lines of floral development. In the Convolvulaceae, the flowers are actinomorphic with ovary bilocular having two ovules in each loculus or tetralocular having one ovule in each loculus. It is related to the Polemoniaceae, but differs from it by the terminal style and ovary structure. 

> The flowers of the Polemoniaceae tend to be slightly zygomorphic, but the carpels may be two, three or five and ovules few to many in each loculus. The floral plan of the Hydrophyllaceae is similar to that of the Polemoniaceae, except that the ovary is bicarpellary and bilocular or unilocular due to the failure of the large marginal placentae to meet in the centre.

> Critical studies of the morphology of the order Personales reveals that Verbenaceae and Labiatae are very closely related, similarly Acanthaceae, Bignoniaceae, Pedaliaceae and Martyniaceae are related; Scrophulariaceae, Orobanchaceae, Lentibulariaceae, Gesneriaceae bear close relationship.

Floral range of Tubiflorean families:-

1. Convolvulaceae:- Flowers actinomorphic hypogynous, corolla funnel shaped to semi-tubular, rotate, tetracyclic, calyx persistent, ovary bicarpellate, often with false septa. Stamens-5. predominantly twining herbs or shrubs, with milky latex often. 

2. Solanaceae:- Flowers as above, calyx the same as above but consisting of almost free sepals. Ovary with false septa sometimes, carpels are oblique. Stamens-5. Predominantly herbs, rarely shrubs. No milky latex.

3. Nolanaceae:- Flowers actinomorphic bisexual, pentamerous, corolla similar to Convolvulaceae in aestivation. Stamens-5. Ovary pentacarpellary with longitudinal septa. Fruit like nutlet.

4. Polemoniaceae:- Flowers bisexual, actinomorphic or slightly zygomorphic; corolla mostly tubular, aestivation of the petals contorted. Ovary with 3- carpels, rarely with 5 or 2 carpels, mostly trilocular, rarely bi- or pentalocular, placentation axile. Predominantly herbs.

5. Hydrophyllaceae:- Flowers bisexual, actinomorphic. Corolla rotated, gamo with various shaped (bell or funnel), Petals imbricate. Ovary bicarpellary, bilocular, sometimes apparently unilocular, placentation axile usually, tending to be parietal. Herbs. 

6. Boraginaceae:- Flowers bisexual, actinomorphic, rarely zygomorphic. Corolla bell shaped or tubular or funnel shaped, petals imbricate, rarely contorted. Ovary of 2 carpels, originally two celled but finally separating into 4 one ovuled portions with gynobasic style, style rarely terminal. Predominently herbs.

7. Scrophulariaceae:- Flowers usually medianly zygomorphic, stamens usually 4, didynamous rarely only 2. Carpels, median; ovules numerous on thick axile placenta. Calyx persistent. Endosperm present.

8. Orobanchaceae:- Flowers zygomorphic, corolla bilabiate or personate. Stamens 4, didynamous. Parietal placentation. Endosperm present.

9. Lentibulariaceae:- Flowers zygomorphic, corolla personate. Stamens-2.Anthers monothecal. Ovules many on free central placenta. Endosperm absent. ……………………..

10. Bignoniaceae:- Flowers zygomorphic, corolla bilabiate or irregular campanulate, Stamens 4, didynamous. Ovary bilocular, rarely unilocular. Axile placentation. Endosperm present or scanty.

11. Acanthaceae:- Corolla bilabiate. Stamens 4 or 2; anthers spurred or hairy. Pollen various shaped. Placentation axile, ovule on retinacula. Endosperm absent.

12. Verbenaceae:- Corolla bilabiate. Calyx persistent and 5-lobed. Stamens 4, didynamous or sometims 5, rarely 2. Ovule 1 in each locule.

13. Labiatae:- Corolla bilabiate. Calyx persistent, bilabiate usually, many toothed. Stamens 4 or 2, connective much developed. Style gynobasic. Ovules 4 in apparently 4-celled ovary.

Helobieae:-

> Helobieae or helobiales is a primitive taxon. It is also known as by Najadales or Fluviales.

> This is characterized by the aquatic or marshy habitats, often completely submerged, flowers hemicyclic to cyclic, actinomorphic, bisexual to unisexual, stamens 1 to many polyandrous, carples free and helobial endosperm.

> Helobieae represents the Engler’s second order of Monocotyledoneae. It includes seven families namely - Potamogetonaceae, Najadaceae, Aponogetonaceae, Scheuchzeriaceae, Alismataceae, Butomaceae and Hydrocharitaceae.

> Helobieae is considered as the most primitive taxon in the Monocotyledons. There are some reasons of primitiveness –

i. Floral parts are free and disposed in many whorls.

ii. Abortion of perianth and reduction in number of stamens of certain members of the family Najadaceae.

iii. Number of stamens and carpels are many having transition from the spiral to whorled arrangement.

iv. Occurrence of wide lamina like filaments with basifixed anthers in the Juncaginaceae and Potamogetonaceae.

v. Presence of laminal placentation in some members of family Alismataceae and Hydrocharitaceae.

vi. Incomplete closure of carpels in certain members of the family Hydrocharitaceae.

> Cronquist (1968) created three orders and twelve families for Helobial plants:

i. Alismatales:- Butomaceae, Limnocharitaceae, Alismataceae.

ii. Hydrocharitales:- Hydrocharitaceae.

iii. Najadales:- Aponogetonaceae, Scheuchzeriaceae, Juncaginaceae, Najadaceae, Potamogetonaceae, Ruppiaceae, Zannichelliaceae, Zosteraceae.

> Stebbins (1974) supported Cronquist (1968) system but Takhtajan (1969) included two extra families namely Posidoniaceae and Cymodaceae under the Najadales.

> Dahlgren (1975) removed the Butomaceae from Alismatales and placed in the Hydrocharitales along with the Hydrocharitaceae and Aponogetonaceae; here the Najadales was meant to accommodate the Najadaceae and seven families viz., Scheuchzeriaceae, Juncaginaceae, Potamogetonaceae, Zosteraceae,

Posidoniaceae, Zannichelliaceae and Cymodoceaceae.

> Thorne (1976) accepted three orders and ten families:

i. Alismatales:- Butomaceae, Alismataceae and Hydrocharitaceae.

ii. Zosterales:- Aponogetonaceae, Scheuchzeriaceae (including Juncaginaceae), Potamogetonaceae, Posidoniaceae, Zannichelliaceae, Zosteraceae.

iii. Najadales:- Najadaceae.

> Hutchinson (1969) placed them in six orders - Butomales, Alismatales, Juncaginales, Aponogetonales, Potamogetonales and Najadales. 

> Takhtajan (1980) included Alismataceae, Butomaceae and Hydrocharitaceae in the order Alismatales while the other families have been segregated into a separate order Najadales, while Cronquist kept them in three orders- Alismatales, Hydrocharitales and Najadales, all in subclass Alismatidae.

> Dahlgren and Clifford (1982) proposed the Hydrocharitales for the Butomaceae, Aponogetonaceae, Hydrocharitaceae (including Thalassiaceae and Halophilaceae), the Alismatales for the Alismataceae (including Limnocharitaceae) and the Zosterales for the Scheuchzeriaceae, Juncaginaceae, Najadaceae, Potamogetonaceae (including Ruppiaceae), Zosteraceae, Posidoniaceae, Cymodoceaceae and Zannichelliaceae.

> In the Helobiae both Potamogetonaceae and Najadaceae are very advanced in terms of evolution. According to Engler and Rendle family Najadaceae is the earliest family in terms of evolution.