In this article we will discuss about the classification of Sarraceniales. According to Engler, Sarraceniales consists of three families:- 1. Sarraceniaceae 2. Nepenthaceae 3. Droseraceae.
Family # 1. Sarraceniaceae:
Sarraceniaceae are perrenial herbs of marshy places. Leaves are radical, rosulate, tubular, usually with a small terminal lamina and retrorsely hairy within, often winged. Flowers solitary on a central scape or racemose, actinomorphic, bisexual, hypogynous, usually spirocyclic and pentamerous. Sepals 5 or rarely upto 9, free, imbricate, persistent, often petaloid. Petals 5, free, or absent.
Stamens numerous, free, anthers 2-celled, dehiscing longitudinally. Ovary superior, of 3-5 united carpels, 3-5-locular, usually 3-5-lobed, with numerous ovules on axile placentation; style lobed at the apex or expanded like an umbrella over the stamens; stigmas situated beneath the tips of the lobes; ovules anatropous.
Fruit a loculicidal capsule; seeds minute, with small embryo and soft fleshy endosperm; testa membranous and winged.
The leaves are modified to form pitchers, or ascidium. The upper part of the pitcher is prolonged into a lid or operculum. According to some the pitcher is the petiole and the lid is the leaf-lamina. Baillon considers the pitcher to be the modified lamina and the lid is nothing but an apical outgrowth of the lamina.
This view is generally accepted. The pitcher has a velvety smooth slippery zone inside near the mouth. Then there is the glandular zone and last is the absorptive zone bearing reflexed hairs and filled with fluid rich in proteolytic enzyme.
The body of the captured insect is digested by the fluid and absorbed by the glands on the pitcher walb In Sarracenia the pitcher bulges out from a narrow base and has a more or less deltoid lid which is often brightly coloured and possesses nectar secreting glands. In Darlingtonia the pitcher is about a metre long gradually widening upwards and has a lid which is forked like a fish-tail.
The family contains 14 species only under 3 genera which are restricted in their distribution to eastern N. America. It is related to the other two families of the order and probably originated with the other two families from the Ranales.
Hutchinson considers that Sarraceniaceae and Droceraceae are close together and originated from Saxifragales while Nepenthaceae is not closely related with these two families and originated from Ranales.
Family # 2. Nepenthaceae:
Nepenthaceae are herbaceous or shrubby plants, often climbing by means of tendrilar leaf-apex. Leaves are alternate, simple, sub-sessile or sessile, with a linear or lanceolate blade and a prolonged apex forming a tendril; the tendril usually terminates in a cylindrical or urceolate pitcher or ascidium with a lid or operculum; stipules absent. Plants are dioecious; flowers borne in axillary racemes or panicles, actinomorphic? hypogynous.
Perianth in 2 whorls, segments 2 in each whorl arranged crosswise, all similar and sepaloid, free, rarely perianth members 3 or 5-6; imbricate, glandular inside and hairy outside. Stamens 4-24, monadelphous in a column; anthers distinct, 2-celled, dehiscing longitudinally, extrorse; pollens in tetrads.
Ovary superior, 4-carpelled and 4-chambered; rarely 3-carpelled and 3-chambered; ovules many, anatropous, on axile placentation; style small and stout or absent, stigma discoid. Fruit an elongated loculicidal capsule; seeds many, filiform, ascending and imbricate; embryo straight embedded in a thin layer of fleshy endosperm.
The pitcher has a recurved fluted rim and a lid which is often brightly coloured and variously margined; nectar is secreted on the rim, at the mouth of the pitcher and often at base of the lid.
The pitcher contains a fluid with a proteolytic enzyme secreted by the glands lining the lower portion of wall. The insects falling into the pitcher gets drowned in the fluid and is digested, the soluble proteid being ultimately absorbed by the walls of the pitcher.
The family contains only 1 genus with over 60 species (according to some 2 genera Nepenthes and Anurosperma) distributed in the eastern tropical zone from Madagascar to New Caledonia and occurring more in Malaysia. In India N- khasiana Linn, is found to grow in and around Shillong in Meghalaya.
The family is closely related to Sarraceniaceae and Droseraceae and has been placed in the order Sarreceniales along with these 2 families by most authors. Takhtajan considers that Nepenthaceae is allied to Droseraceae but is not at all related to Sarraceniaceae.
According to Hutchinson Nepenthaceae is allied to Aristolochiaceae and therefore includes Nepenthaceae in Aristolociales while Sarraceniaceae and Droseraceae are placed in Sarraceniales having probable affinity with Saxifragales.
The family is of no economic importance but plants are often cultivated as curiosities.
Family # 3. Droseraceae:
Droseraceae are annual or perennial herbs or undershrub’s, often with perennial rhizome, inhabiting marshy places. Leaves are alternate, rarely whorled near the base forming a rosette, usually covered with viscid glands or tentacles for catching small insects; often circinate in bud; membranous stipules often present. The inflorescence is a spike or a raceme or sometimes a cincinnus, or flowers may be solitary.
Flowers are bisexual, actinomorphic, hypogynous, pentamerous or tetramerous. Sepals 4-5, connate near base, imbricate, persistent. Petals usually 5, free, convolute. Stamens 5-10 or more, in one or more pentamerous whorls, free or rarely connate below; anthers extrorse, 2-celled, cells often divergent and with broad connective, dehiscing longitudinally; the pollens are in tetrads.
Ovary superior or half-inferior, 3-5-carpelled, syncarpous, unilocular with numerous anatropous ovules on 3-5 parietal placentas; rarely ovules few on basally free central placenta; styles 3-5, usually free, often forked or branched with capitate stigmas; very rarely the ovary 3-5-chambered with axile placentation. Fruit a loculicidal capsule; seeds numerous with straight embryo and granular endosperm.
The leaves have 2 kinds of glands, the stalked glands that always secrete a sticky fluid and the sessile glands which secrete a digestive ferment only when stimulated by a nitrogenous matter. Drosera and Drosophyllum have such stalked glands or tentacles.
They attract the small insects and keep them attached to the leaves by means of the viscid substances. They are capable of movement or curvature and bend down over the body of the captured insect from all sides to hold it tightly. The digestive fluid secreted by the sessile glands absorb the decomposed body of the insect.
Aldrovanda and Dionaea have different mechanism for capturing their prey. The leaf has a broad lamina on a distinct petiole. The lamina is divided into two halves which can fold and close along the midrib ‘on slight stimulus and trap an insects alighting on the surface of the lamina. The digestive fluid secreted by the glands on the surface of lamina gradually absorb the decomposed body.
Dionaea is a small herb with a rosette of basal leaves. It has a perennial rhizome. Aldrovanda is a rootless submerged herb with slender stem and branches and a whorl of leaves at each node. Drosophyllum has a short woody stem which is often branched. The long narrow leaves are crowded at the apical part of stem and branches and the persistent leaf bases of the older leaves cover the lower part of the stem.
Drosophyllum and Dionaea have primary root, but in most Drosera species primary root is absent and protocorm like structure develops from the hypocotyl bearing filiform rhizoid-like structure.
The family consists of 4 genera only of which Drosera has 84 species distributed over wide areas in the 2 hemispheres having quite a number in Australia.
Other 3 genera are monotypic. Drosophyllum is N. American; Dionaea is confined to western Mediterranean region while Aldrovanda occurs in Europe, Asia and Australia. Several species of Drosera occur in India, e.g. D. indica L., D. burmannii Vahl., D. peltata Sm. etc. Aldrovanda vesiculosa L. which has a very wide distribution is found in Dacca. It was reported from Calcutta about a century ago but is no longer found.
The leaves of Drosera yield a violet dye. As to the affinity of the family different opinions have been expressed. Engler, Rendle and others consider the 3 families Sarraceniaceae, Nepenthaceae and Droseraceae closely related and place them in a single order next to Rhoedales. Cronquist also considers that the 3 families are allied to one another.
Diels, Wettstein, and few other placed Droseraceae in the Parietales for having parietal placentation. Hutchinson and others following Lindley consider the family to be close to Saxifragaceae. It is, however, agreed by most authors that the 3 families are closely related and that Sarraceniales like Rhoedales has been derived from Ranales.
