Clonal Growth Forms in Eastern Ladakh, Western Himalayas: Classification and Habitat Preferences

Abstract

Earlier observations that plant clonality, i.e., production of potentially independent offspring by vegetative growth, increase in importance in cold climates such as in arctic and alpine regions, have been recently questioned. However, lack of data obtained using a comparable methodology throughout different regions limit such comparisons. Here we present a classification of clonal growth forms for vascular plants from East Ladakh (an arid mountain range in NW Himalaya, India), and assess the relationship of these forms with multiple environmental gradients. Based on field assessment of clonality in 540 species we distinguished 20 growth forms, which were then grouped into four broader space occupancy strategies. Occurrence in communities and relationship with environmental characteristics and altitude were analyzed using multivariate methods. The most abundant growth form was represented by non-clonal perennial species with a pleiocorm having short branches, prevailing in steppes, Caragana shrubs and screes. The most abundant clonal species were those with very short epigeogenous rhizomes, such as turf graminoids prevailing in wet Kobresia grasslands. Two principal environmental gradients, together with several abiotic variables, affected space occupancy strategies: moisture and altitude. Non-spreading integrators prevailed on shaded rocky slopes, non-spreading splitters in wet grasslands and spreading splitters at the wettest sites. Spreading integrators were the least frequent strategy predominantly occurring at the most elevated sites. Because relevance of clonality decreased with altitude and different communities host different sets of clonal growth strategies, comparison with other cold climate regions should take multiple environmental gradients into account.

Appendices

Appendix 1

Identification key of clonal growth forms of vascular plants in eastern Ladakh, Western Himalayas

• 1a stems only above-ground................................................................................................................2

• 1b stems also below-ground................................................................................................................7

• 2a neither adventitious roots nor buds present on roots (non-clonal plants)...............................................3

• 2b horizontal rooting stem...................................................................................................................4

• 2c plant fragments...............................................................................................................................5

• 3a annual and biennial herbs (“Microula tibetica” type)

• 3b trees (“Juniperus semiglobosa” type)

• 3c cushion plants (“Thylacospermum caespitosum” type)

• 4a horizontal stems short-lived (up to two growing seasons)

• Short-lived horizontal rooting stems on or above soil surface:

• short-lived herbaceous clonal growth organ rooting in the soil and providing connection between offspring plants or formed by creeping axis; nodes on stem bearing leaves, internodes usually long, stem serving as a storage organ and bud bank; vegetative spreading usually fast and persistence low (“Halerpestes sarmentosa” type)

• 4b horizontal stems long-lived (more than two growing seasons)

• Long-lived horizontal rooting stems on soil surface:

• long-lived, usually woody, clonal growth organ formed by creeping axis, rooting in the soil; nodes of youngest parts bearing leaves, internodes shorter than in short-lived horizontal stems; stem serving as a storage organ and bud bank; vegetative spreading slow and persistence high (“Thymus linearis” type)

• 5a plant fragments specialized for overwintering (turions)

• Turions:

• detachable over-wintering buds (usually in water plants) composed by tightly arranged leaves filled with food reserves; turions, developing axially or apically and needing vernalisation to re-growth (“Potamogeton amblyphyllus” type)

• 5b unspecialized plant fragments

• Plant fragments of stem origin:

• detached parts of shoot with rooting ability (“Potamogeton perfoliatus” type)

• 5c detachable offspring........................................................................................................................6

• 6a offspring in inflorescence (pseudovivipary)

• Plantlets (pseudovivipary):

• meristem normally develops into a flower, but forms vegetative buds (plantlets, bulbils, root or stem tubercules), which are sometimes soon detached from the parent plant; alternatively the entire inflorescence falls off and the plantlets root at the soil surface; offspring size similar to seedlings (“Bistorta vivipara” type)

• 6b offspring in axils of leaves

• Axillary buds:

• small vegetative diaspores produced in axils of leaves on stems above-ground formed by axillary buds subtended by small storage organ of stem, root (tubercule) of leaf (bulbil) origin; buds soon shed from mother plant, beginning to grow immediately; resembling seedlings in size (“Saxifraga cernua” type)

• 7a below-ground stems lacking adventitious roots and roots lacking adventitious buds.............................................................................................................................................8

• 7b below-ground stems possessing adventitious roots and/or roots possessing adventitious buds.............................................................................................................................................9

• 8a long below-ground stems (pleiocorm)

• Pleiocorm having long branches:

• plant possessing a primary root system lacking adventitious roots and buds; tap root serving as storage organ; bud bank situated on perennial stems with long (more than 10 cm) branches serving as vascular link between shoots and primary root; non-clonal plants (“Saussurea gnaphalodes” type)

• 8b short below-ground stems (pleiocorm)

• Pleiocorm having short branches:

• plant possessing a primary root system lacking adventitious roots and buds; tap root serving as storage organ; bud bank situated on perennial stems with short (less than 10 cm) branches serving as vascular link between shoots and primary root; non-clonal plants (“Arnebia euchroma” type)

• 9a roots with adventitious buds.........................................................................................................10

• 9b roots without adventitious buds....................................................................................................11

• 10a adventitious buds on main root

• Main root with adventitious buds:

• main root (include hypocotyle) forming adventitious buds spontaneously or after injury; clonal growth usually only after fragmentation of main root (“Parrya nudicaulis” type)

• 10b adventitious buds on horizontal creeping roots

• Horizontal roots with adventitious buds:

• branches of main root and adventitious roots forming adventitious buds spontaneously or after injury; roots serving as bud bank and vascular connection between offspring shoots; lateral spread usually extensive; persistence differing among species (“Ptilotrichum canescens” type)

• 11a below-ground stems lacking specialized storage organs............................................................12

• 11b below-ground stems possessing specialized storage organs, stems sometimes reduced.............15

• 12a stems formed below-ground (hypogeogenous rhizomes)...........................................................13

• 12b stems formed at soil surface and older parts placed below-ground (epigeogenous rhizomes)...................................................................................................................................14

• 13a hypogeogenous rhizomes with short increments (less than 10 cm)

• Short hypogeogenous rhizomes:

• perennial organs of stem origin formed below-ground; rhizome usually growing at a species specific depth, periodically becoming orthotropic and forming above-ground shoots; horizontal part of the rhizome bearing bracts, some roots and possessing short internodes; vegetative spreading intermediate; persistence differing considerably among species (“Leontopodium ochroleucum” type)

• 13b hypogeogenous rhizomes with long increments (more than 10 cm)

• Long hypogeogenous rhizomes:

• perennial organs of stem origin formed below-ground; rhizome usually growing at a species-specific depth, periodically becoming orthotropic and forming above-ground shoots; horizontal part of the rhizome bearing bracts, some roots possessing long internodes; vegetative spreading fast; persistence differing considerably among species (“Poa tibetica” type)

• 14a Short epigeogenous rhizomes:

• perennial organ of stem origin formed above-ground; its distal part covered by soil and litter or pulled into the soil by contraction of roots; nodes bearing green leaves; internodes usually short; rhizomes bearing roots and serving as a bud bank and storage organ; vegetative spread low (up to one cm per year); persistence usually low; typical of tussock grasses (“Festuca kashmiriana” type)

• 14b Medium long epigeogenous rhizomes:

• perennial organ of stem origin formed above-ground; its distal part covered by soil and litter or pulled into the soil by contraction of roots; nodes bearing green leaves; internodes usually short; rhizomes bearing roots and serving as a bud bank and storage organ; vegetative spread low (up to a few cm per year); persistence usually low (“Cremanthodium ellisii” type)

• 14c Long epigeogenous rhizomes:

• perennial organ of stem origin formed above-ground; its distal part covered by soil and litter or pulled into the soil by contraction of roots; nodes bearing green leaves; internodes usually short; rhizomes bearing roots and serving as a bud bank and storage organ; vegetative spread low (up to a few cm per year); persistence usually long, resulting in a large preserved rhizome system (“Biebersteinia odora” type)

• 15a storage in leaves

• Bulbs:

• storage and perennation organ consisting of storage leaves and shortened stem base; stem providing bud bank and connection between offspring shoots; lateral spread low (“Lloydia serotina” type)

• 15b storage in stem

• Stem tubers:

• below-ground, usually short-lived storage and regenerative organ of shoot origin; lateral spread high in the case of offspring tubers formed on hypogeogenous rhizome, persistence usually low (“Potamogeton filiformis” type)