Petrosaviales, a minimal order grouped within the lilioid monocotsWhat is monocots?Angiosperm having only one cotyledon. Cotyledon is seed leaf; the first leaf (or set of leaves) to appear during the early development of a seedling., are found in eastern and southeastern Asia. plants of Petrosaviales have no laticifers and vessels in the axial system and possess simple, small, reduced (or absent) leaves. The flowers are bisexual, actinomorphicWhat is actinomorphic?A characteristic of the flower exhibiting radial symmetry such as starfish or Daisy flower; capable of being bisected into identical halves along more than one axis, forming mirror images. Opposite is Zygomorphic., and typically with six persistent tepals. Japolinorion osense and Petrosavia sakuraii are example species of the Petrosaviales order.
Petrosaviales Families
Petrosaviales has 1 family (Petrosaviaceae), 2 genera, and 4 species[1]. The APG IV system placed Petrosaviaceae family under Order Petrosaviales. Petrosaviaceae has two genera, Japonolirion and Petrosavia. Genus Japonolirion has one species while Petrosavia has 3 species.
Petrosaviales Distribution
Species of Petrosaviales are found in habitats with high elevations. The genus Japonolirion has only one species found only in Japan. Habitats of the Japonolirion species involve grasslands, wetlands, and alpine meadows of Northern Japan (meadows around Mt. Shibutsusan) and Teshio province. Genus Petrosavi a members are distributed in Eastern and southeastern Asia. They are found in Eastern India, Japan, Southern China to West Malesia.
Petrosaviales Characteristics
Below are the characteristics of Petrosaviales plants.
- Plant type: Members are herbs. The species are photosynthetic (Japonolinorion) or rare achlorophyllous, mycoheterotrophic (Petrosavia).
- Stem: They are plants without laticifers. Axial anatomy involves the absence of vessels in the axial system.
- Leaves: The leaves are small, simple, and alternate (Japonolirion). Petrosavia has reduced to absent leaves. The leaves on the rhizomeWhat is rhizome?An underground stem, with nodes and short to elongate internodes. are scaly.
- Flowers and inflorescences: The flowers are bisexual and actinomorphic. The flowers are small (2-4 mm)[2] and regular. Inflorescence involves bracteates racemes or corymbs, bracteoles sublateral.
- Sepals and petals: Flowers have six persistent tepals; free. Septal nectaries are present.
- Stamens and carpels: The stamen filaments are free or partly attached to the perianth. The carpels are typically 3, sometimes connate at the base only.
- Ovary and fruit: The ovary is superior to partly inferior. The fruit is a follicular or septicidal capsule.
- Seeds: The seeds are small and numerous. CotyledonWhat is Cotyledon?A seed leaf; the first leaf (or set of leaves) to appear during the early development of a seedling. is 1. The microsporogenesis is simultaneous.
Petrosaviales Flowers and Reproduction
Petrosaviales flowers are pedicellateWhat is pedicellate?Borne on a pedicel; a flower characterized by having a stalk is also known as pedunculate or pedicellate; opposite is sessile (i.e., no stalk); with bracteates racemes. There are six tepals (persistent); 2 are whorled. Carpels are three, and septal nectaries are also present.
- Japonolirion flowers are aggregated in racemes with racemose as a vital inflorescence unit. The flower is simple, solitary, erect, several to many-flowered. The size is minute to small with a perianth measurement of 2.5-3 mm long.
- ‘Petrosovia species[3] inflorescence is also a raceme (sometimes with or without corymbose). The flowers are small with a broadly ovoid ovary.
- The saprophytic species Petrosavia sakuraii is adapted to self-pollination[4]. Therefore, there is a very high selfing rate; this includes insect-mediated pollination. This manner of sexual reproduction favors the survival of this species, possibly having severe resources limitation.
- However, chances of cross-pollination by small bees of Lasioglossom and other insects still happen. However, cross-pollination only offers a low out-crossing frequency, and the insect’s flower visitation is not so frequent.
Petrosaviales Genus Differences
Order Petrosaviales only has one family (Petrosaviaceae) under it. Petrosaviaceae, in turn, is divided into 2 genera. The following characteristics differentiate the two genera from each other.
Japonolirion
- It has chlorophyll. Plants are autotrophic.
- Stigma is decurrent.
- Stamen filaments are free.
- Fruit is a septicidal capsule.
- Ovules are 4-12 per carpel.
- The nucleus is symmetrical[5] on the endospermWhat is endosperm?An embryonic nutritive tissue formed during double fertilization by the fusion of a sperm with the polar nuclei.‘s first division.
Petrosavia
- It lacks chlorophyll. Plants are saprophytic.
- Stigma is subcapitate.
- Stamen filaments are partly attached to the perianth.
- Fruit is a follicle.
- Ovules are many per carpel.
- The nucleus is asymmetrical on the endosperm’s first division.
Petrosaviales Example Species
There are only 4 species under Order Petrosaviales. There is one species under Japonolirion:.
- Japonolirion osense
The three Petrosavia plants are:
- Petrosavia sakuraii
- Petrosavia sinii
- Petrosavia stellaris
