Rungia longifolia

An endemic herb under shade and often close to streams in forests of moist lowlands. Flowering from March to April.
  

Heterotis rotundifolia

Native plant of tropical West Africa. Probably escaped from cultivation and naturalized in the wet lowland areas. 

හල් බැඹිය[Hal bebiya] (Cipadessa baccifera)

Common indigenous shrub or small tree occurs along forest edges, thickets, ravines and rock crevices in dry lowland and intermediate zone. Flowering throughout the year. 

Torenia anagallis [Syn: Lindernia anagallis]

An indigenous small herb common in harvested paddy fields and pond edges in wet lowlands and up to 550 m altitude in the wet hills. It usually grows in association with Lindernia rotundifolia. Flowering throughout the year.

Sonerila silvatica

Locally common endemic erect herb occurs in southwestern wet lowland forests. Sonerila silvatica grows sympatrically with the Sonerila rhombifolia.

Lollipop plant/Golden shrimp plant (Pachystachys lutea)

An introduced ornamental shrub native to Central and South America from El Salvador to Peru. Cultivated in gardens. 

හීන් ඇඹිල්ල[Heen Abilla] (Antidesma alexiteria)

Common native shrub or small tree distributed in both wet and dry lowlands. 

Dysphania palmyra

Expanse - 7 - 8 cm

Reference - The Lepidoptera of Ceylon - F. Moore, F.Z.S. Vol 3 Page 422- 423.

Larval host plant - දවට (Carallia brachiata)

External Links - http://www.inaturalist.org/listed_taxa/3412330

Spermacoce exilis [Spermacoce mauritiana]

An introduced annual herb native to tropical America. Naturalized in shady places and among grass (in the wet lowlands ?)

Phyllanthus pulcher

Small shrub native to tropical Southeast Asia. Introduced and now an invasive in disturbed rain forest habitats of Kalutara and Ratnapura districts.

Justicia ceylanica

Rather common endemic herb occurs in southwestern wet lowlands and mid country forests, often beside rocks and along streams. Flowering from February to March and again from August to November.

Sesamum radiatum

An introduced erect annual herb occurs in waste places from north of Colombo to Negombo. Sesamum raditum is  native to tropical West Africa. Flowering from May to August or probably throughout the year. Trimen noted that "no doubt it is spread from Botanic gardens".

Nyctemera lacticinia

Location - Sigiriya

Expanse - Male: 3.8cm cm Female: 4.5cm

Reference - The Lepidoptera of Ceylon - F. Moore, F.Z.S. Vol 2 Page 47- 48.

Ecology - Day flier

External links : http://www.inaturalist.org/taxa/124131-Nyctemera-lacticinia

කන් කුඹල[Kan kubala] (Cynanchum tunicatum)

Rather uncommon indigenous herb twining in hedges and fences of the dry zone. Flowering from November to March.

Vincetoxicum bracteatum [Syn: Tylophora pauciflora]

Rather rare indigenous twining plant growing mainly in the dry lowlands. Also cultivated in wet and intermediate zone home gardens. 

අඟුණ/තිත්ත අඟුණ/අනුක්කොල/කිරි අඟුණ(Wattakaka volubilis [Syn: Dregea volubilis])

An indigenous twiner climbing in trees and shrubs, distributed in dry lowlands up to about 1000 m a.s.l. Flowering from March to April and again rarely from August to November.  Leaves edible and eaten as curries. Leaves also used in traditional medicine.

Trichosanthes scabra [Syn: Gymnopetalum scabrum/Gymnopetalum integrifolium]

Largely creeping and climbing native annual herb common in the waste places of dry and intermediate zones up to about 200 m altitude. Flowers opening in the evening. 

Dotted Sable (Bocchoris inspersalis)

Location - Indhikada Mookalana forest reserve.
External Links - http://www.inaturalist.org/listed_taxa/3413230
                         https://en.wikipedia.org/wiki/Bocchoris_inspersalis

Struchium sparganophorum

An introduced erect herb native to tropical America. It was first collected at Meerigama in November 1931. Rather uncommon naturalized weed in moist ground and ditches in South and Western lowland areas of the island. Flowering from July to March. 

එළ මල් [Ela mal]/White-ginger Lily/Butterfly ginger (Hedychium coronarium)

Native large herb of India and Malaysia. Perhaps also native to the Sri Lanka*. Cultivated and also naturalized in the wet lowlands and hill country up to about 1500 m altitudes

* Illustrated field guide to the flowers of Sri Lanka - J & J de Vlas