Helobieae or helobiales : Salient features, floral & family diversity.

Helobieae or helobiales : Salient features, floral & family diversity.

Salient features of Helobieae or helobiales
Floral diversity in Helobieae or helobiales

Diversity of families in Helobieae or helobiales

Phylogeny of Helobieae or helobiales

Families Historically Included in Helobieae/Helobiales,
Alismataceae, Hydrocharitaceae

1. Helobieae / Helobiales : Salient features, floral & family diversity and phylogeny Subheadings - (i) Salient features of Helobieae or helobiales (ii) Floral diversity in Helobieae or helobiales (iii) Diversity of families in Helobieae or helobiales (iii) Phylogeny of Helobieae or helobiales

2. Helobieae / Helobiales : Salient features, floral & family diversity and phylogeny Dr . Praveen Mohil Assistant Professor Department of Botany University of Rajasthan Jaipur-302004

3. Other names Helobiales Helobie Najadales Fluviales @monocot

4. Why this Taxon is so special ? Ans. The order is important from the consideration of some taxonomists who believe that other orders of Monocotyledons were derived from it . There are some supporting features like aquatic habit representing submerged to semi-submerged condition, large embryo with large hypocotyl for storing food, absence of endosperm in seeds and free carpels ( apocarpy ).

5. Introduction Monocot taxon Helobieae / helobiales is a primitive taxon. It is also known as by Najadales or Fluviales . This term was historically used to refer to a group of monocotyledonous aquatic plants. " Helobieae " and " Helobiales " refer to outdated classifications in the taxonomy of aquatic plants. These terms are not commonly used in modern botanical nomenclature.

6. (i) Salient features of Helobieae or helobiales Taxon Helobieae is considered most primitive ones by most of the systematist . Plants in this group were characterized by their adaptation to aquatic environments and included families such as Alismataceae , Hydrocharitaceae and others. Helobieae represents the Engler’s second order of Monocotyledoneae . It includes sevenfamilies namely Potamogetonaceae , Najadaceae , Aponogetonaceae , Scheuchzeriaceae , Alismataceae , Butomaceae and Hydrocharitaceae . Helobieae is considered as the most primitive taxon in the Monocotyledons.

7. (i) Salient features of Helobieae or helobiales There are some reasons of primitiveness – (i) Floral parts are free and disposed in many whorls ….. free vs united K,C or Poly vs Gamo (ii) Abortion of perianth and reduction in number of stamens of certain members of the family Najadaceae …………………….reduction ∝ advancement with full purpose (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 .

8. (ii) Floral diversity in Helobieae or helobiales ……A 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. The floral diversity within the group historically referred to as Helobieae or Helobiales , now largely classified under the order Alismatales , is quite extensive . These aquatic plants exhibit a variety of floral structures and reproductive strategies, adapted to their water-based habitats .

9. (ii) Floral diversity in Helobieae or helobiales ………..B Here's an overview of the floral diversity in some key families within this group: Key Families and Their Floral Diversity Floral Characteristics@ Alismataceae -Typically have flowers with 3 sepals and 3 petals. The flowers are often bisexual, containing both male (stamens) and female (pistils) reproductive organs. Flowers are usually arranged in inflorescences like racemes or panicles. Floral Characteristics@ Hydrocharitaceae - Flowers can be unisexual or bisexual. Flowers generally have three sepals and three petals, often white or yellow. Floral Characteristics@ Butomaceae - Butomus umbellatus has umbels of pink flowers. Each flower has 03 sepals and 03 petals, numerous stamens, and a central cluster of carpels .

10. (ii) Floral diversity in Helobieae or helobiales ……………C Floral Characteristics@ Juncaginaceae - Flowers are small and often arranged in spikes. Typically have 06 tepals (undifferentiated sepals and petals).Flowers are generally wind-pollinated . Floral Characteristics@ Potamogetonaceae - Flowers are often small, inconspicuous, and arranged in spikes or clusters.Typically lack petals; instead, they have 04 tepals . Adapted for water pollination ( hydrophily ). Floral Characteristics@ Aponogetonaceae - Flowers are showy, with species like Aponogeton distachyos having white, fragrant flowers that float on the water surface.Inflorescences are often spikes that emerge above the water. Their varied and specialized floral structures reflect their ecological roles and pollination strategies, contributing to the rich biodiversity of aquatic ecosystems.

11. (iii) Diversity of families in Helobieae or helobiales The historical classification of Helobieae or Helobiales encompassed a variety of aquatic plant families, which are now largely reclassified under the order Alismatales . Key Families Historically Included in Helobieae / Helobiales- Alismataceae , Hydrocharitaceae,Butomaceae , Juncaginaceae , Potamogetonaceae and Aponogetonaceae . In Bentham and Hooker's classification, the order Helobiae (or Helobiales ) included families of aquatic plants. Families in Helobieae ( Helobiales )- According to Bentham and Hooker are Alismataceae , Butomaceae , Hydrocharitaceae , Najadaceae , Juncaginaceae , Potamogetonaceae and Aponogetonaceae Cronquist (1968) created three orders and twelve families for Helobial plants: 1. Alismatales :- Butomaceae , Limnocharitaceae , Alismataceae . 2. Hydrocharitales :- Hydrocharitaceae . 3. Najadales :- Aponogetonaceae , Scheuchzeriaceae , Juncaginaceae , Najadaceae , Potamogetonaceae , Ruppiaceae , Zannichelliaceae , Zosteraceae .  

12. (iii) Diversity of families in Helobieae or helobiales 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: 1. Alismatales :- Butomaceae , Alismataceae and Hydrocharitaceae . 2. Zosterales :- Aponogetonaceae , Scheuchzeriaceae (including Juncaginaceae ), Potamogetonaceae , Posidoniaceae , Zannichelliaceae , Zosteraceae . 3. Najadales :- Najadaceae .

13. (iii) Diversity of families in Helobieae or helobiales 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 ordersAlismatales , 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  

14. (iv) Phylogeny of Helobieae or helobiales Taxon Helobieae is considered most primitive ones by most of the systematist . Wettstein has also given first place to the order Helobieae . Hutchinson splitted Helobieae into several independent orders such as Butomales , Alismatales , Juncaginales , Aponogetonales , Potamogetonales and Najadales . In views of Wettstein and Hutchinson the primitive monocotyledonous order Helobieae was derived from early Ranales ( Dicotyledons ). So Helobieae forms the possible connecting link between Dicotyledons and Monocotyledons . There is possible line of evolution, indicating that Butomoideae , Alismaceae and other monocotyledonous families had their origin from Ranales ( Mitra 1974). 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 . In the other families of group, flowers are confirm to the structure that were derived from the regular trimerous types having the formula of P 3+3, A 3+3, G 3+3. There is trend of multiplication of the members of the androecium and gynoecium either by doubling or by increasing the number of whorls.

15. (iv) Phylogeny of Helobieae or helobiales Modern Classification The families once grouped under Helobieae or Helobiales are now placed in different orders and clades within the monocots. Alismataceae : This family is now placed under the order Alismatales , which includes other related families of aquatic plants. Hydrocharitaceae : This family is also included in the order Alismatales . The order Alismatales now encompasses a wide range of aquatic plants, including those previously categorized under Helobieae and Helobiales . Key Families in Alismatales - Alismataceae , Hydrocharitaceae , Araceae The phylogenetic relationships within Alismatales are based on DNA sequence data, including chloroplast, mitochondrial, and nuclear genomes.

16. (iv) Phylogeny of Helobieae or helobiales Evolutionary Insights Molecular Evidence : Phylogenetic studies using chloroplast DNA sequences (e.g., rbcL , matK ), nuclear ribosomal DNA, and mitochondrial genes have been crucial in resolving the relationships within Alismatales . These data sets provide robust support for the monophyly of the order and clarify the placement of various families. Morphological Convergence : Many families within Alismatales show convergent evolution of aquatic traits, such as submerged leaves, flexible stems, and specialized pollination mechanisms. These traits have evolved independently in different lineages in response to similar environmental pressures.

17. Cladogram Representation A simplified cladogram of Alismatales , highlighting the key families, might look like this: Alismatales ├── Alismataceae ├── Butomaceae ├── Juncaginaceae ├── Aponogetonaceae ├── Potamogetonaceae └── Hydrocharitaceae This cladogram illustrates the basal position of Alismataceae and the more derived placement of families like Potamogetonaceae and Hydrocharitaceae . Molecular phylogenetic studies have clarified the relationships among these families, demonstrating their monophyletic nature and the evolutionary processes driving their diversity.      

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