[i]Houseplants and their benefits to our health and environment[i]

Stress reducing effects: Scientific research carried out at the University of Twente, The Netherlands - K.Dijkstra, M.E.Pieterse & A.Pruyn has shown stress reducing effects of indoor plants in the built healthcare environment.
Participants exposed to indoor plants in a hospital room reported less stress than those in the control condition. Mediation analysis confirmed that indoor plants in hospital reduces stress through their attractiveness of the room.
A study carried out by Kansas State University compared patients in rooms without plants and with plants.
Patients in rooms with plants request less pain medication, lower heart rates and blood pressure, less fatigue and anxiety and were released from the hospital sooner.

The experience also speeds up the recovery of surgical patients.

Influence of limited visible leafy indoor plants on the psychology, behaviour and health of students at Junior High School in Taiwan - Ke-Tsung Han. Two classes of Sophsomores at a Taiwanese Junior High School (eight grade). A expermental group and control group were surveyed every two weeks after 6 plants were placed at the back of the class room. The expermental group immediately demonstrated significantly stronger feelings of preference comfort and friendliness, they had fewer hours of sick leave and punishment records due to misbehaviour compared with the control group.

A study carried out by the Royal college of Agriculture in Cirencester, England found that attentiveness of students was 70% greater when thought in rooms containing plants and attendance was also higher for lectures given in these classrooms.

Dutch Product Board for Horticulture discovered that when plants were added to offices resulted in decrease fatigue, colds, headaches, coughs, sore throats and flu-symptoms.

Plant physiology - studies has shown that plants can absorb certain organic chemicals and distroy these chemicals by a process called metabolic breakdown.
NASA research (VOCs) - Plants purify the air by removing toxins such as cigarette smoke, benzene and formaldehyde and solvents found in man-made fibres.
I have read that NASA is contemplating decorating their officeswith plants in order to promote a more productive and friendly environment.
Journal of Environmental Horticulture 1996,14(2): 97-100 Dr. Lohr Interior plants may improve worker productivity and reduce stress in a windowless environment.
Journal

Examples & Benefits

Plant Benefit
Spider plant (Chlorophytum comosum) Purifies air removes formaldehyde
Dragon tree (Dracaena marginata)
Philodendron

Boston fern (Nephrolepis exaltata) Humidifies air
( Bostoniensis)

English ivy (Hedera helix) Removes benzene

Peace lily (Spathiphyllum) Removes mold from the air