''Jensenia'' is a bryophyte plant genus in the liverwort

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Pallaviciniaceae Pallaviciniaceae is a widely distributed family of liverworts in the order Pallaviciniales. All species are thallose, typically organized as a thick central costa (midvein), each side with a broad wing of tissue one cell in thickness. All spe ...

. It has been treated as a subgenus of Pallavicinia by several authors, though a set of features seems to set it apart as a genus. The six or seven species of the genus belong to a southern, possibly

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

element.

General characteristics

''Jensenia'' liverworts are

dioicous Dioicy () is a sexual system where archegonia and antheridia are produced on separate gametophytes. It is one of the two main sexual systems in bryophytes. Both dioicous () and monoicous gametophytes produce gametes in gametangia by mitosis rathe ...

. Compared to '' Pallavicinia'' liverworts, their

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms wer ...

grows erect, and branches tree-like, rather than trailing the ground. The thallus is perched on an ascending stipe which grows from a creeping

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

. Slime

papilla Papilla (Latin, 'nipple') or papillae may refer to: In animals * Papilla (fish anatomy), in the mouth of fish * Basilar papilla, a sensory organ of lizards, amphibians and fish * Dental papilla, in a developing tooth * Dermal papillae, part of ...

e are absent from the thallus margin, though locally present elsewhere. The midrib of the thallus is broad but ill-defined.

Reproductive morphology

Male reproductive organs are scattered over the thallus's dorsal surface, while female organs are specifically placed near a bifurcation of the frond. The pseudoperianth, a tube of thallus tissue protecting the

archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...

, is basally fused with the calyptra. Following fertilization, the

sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...

is enveloped by three structures: the cup-shaped involucre, cylindrical pseudoperianth and the calyptra. The

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

surfaces are irregularly fasciated.

References

Pallaviciniales Liverwort genera {{Bryophyte-stub